Linter should raise a warning on invalid Ruby syntax

[dathagerty]

Currently, when a file with invalid syntax is run through the linter, it causes errors. This makes big, unfriendly red modals fill the right side of the editor and is generally user-unfriendly.

This goal of this change is to reduce these errors to a warning for Linter, so the user is alerted to the invalid syntax but does not have large, unfriendly modals disrupting the view of the editor.

[dathagerty]

This is in reference to #92.

[vzamanillo]

Fixed on #121