Don't output "Checking" progress when stdout is piped/redirected

[injust]

Because of #20, I pipe prek's output through a pager like less, or redirect it to a file. However, this appears at the top of the output, after the list of hooks:

Checking ------------------------------------------------------------ 1/19 files
Checking ------------------------------------------------------------ 2/19 files
Checking ------------------------------------------------------------ 3/19 files
Checking ------------------------------------------------------------ 4/19 files
Checking ------------------------------------------------------------ 5/19 files
Checking ------------------------------------------------------------ 6/19 files
Checking ------------------------------------------------------------ 7/19 files
Checking ------------------------------------------------------------ 8/19 files
Checking ------------------------------------------------------------ 9/19 files
Checking ------------------------------------------------------------ 10/19 files                                                                               

Checking ------------------------------------------------------------ 11/19 files                                                                               

Checking ------------------------------------------------------------ 12/19 files                                                                               

Checking ------------------------------------------------------------ 13/19 files                                                                               

Checking ------------------------------------------------------------ 14/19 files                                                                               

Checking ------------------------------------------------------------ 15/19 files                                                                               

Checking ------------------------------------------------------------ 16/19 files                                                                               

Checking ------------------------------------------------------------ 17/19 files                                                                               

Checking ------------------------------------------------------------ 18/19 files                                                                               

Checking ------------------------------------------------------------ 19/19 files                                                                               

When using less, it appears in the terminal as:

  Checking ------------------------------------------------------------ 1/19 files^MChecking ------------------------------------------------------------ 2/19 files^MChecking ------------------------------------------------------------ 3/19 files^MChecking ------------------------------------------------------------ 4/19 files^MChecking ------------------------------------------------------------ 5/19 files^MChecking ------------------------------------------------------------ 6/19 files^MChecking ------------------------------------------------------------ 7/19 files^MChecking ------------------------------------------------------------ 8/19 files^MChecking ------------------------------------------------------------ 9/19 files^MChecking ------------------------------------------------------------ 10/19 files                                                                               ^MChecking ------------------------------------------------------------ 11/19 files                                                                               ^MChecking ------------------------------------------------------------ 12/19 files                                                                               ^MChecking ------------------------------------------------------------ 13/19 files                                                                               ^MChecking ------------------------------------------------------------ 14/19 files                                                                               ^MChecking ------------------------------------------------------------ 15/19 files                                                                               ^MChecking ------------------------------------------------------------ 16/19 files                                                                               ^MChecking ------------------------------------------------------------ 17/19 files                                                                               ^MChecking ------------------------------------------------------------ 18/19 files                                                                               ^MChecking ------------------------------------------------------------ 19/19 files                                                                               ^M

I normally don't see the word "Checking" in prek's output in the terminal, so I'm not sure where this comes from. But it would be preferable to omit this when stdout is redirected.