Change LICENSE files with underscores to adapte cargo-about

[jliu666]

The corresponding LICENSE file cannot be correctly detected by cargo about due to the use of underscores in its filename.

Can the file name be modified?
I will also raise an issue on cargo-about, hoping to adapt to the underline.

[FabianLars]

dashes seem to be more common than underscores so i guess changing the file names is a good idea. hopefully it doesn't break anything else. 😂