Error in Dangerfile

[ConnorSheremeta]

Describe the bug
When Danger checks for changes to the lib and app directories there is an error in the regex.

To Reproduce
Steps to reproduce the behavior:

1. Create a new branch in discovery with change to lib or app directory
2. Wait for Travis to build
3. See error in raw logs and the bot's warning

I think this is showing that there is a problem with the syntax /lib\|app/

Expected behavior
If there is a warning from the bot it should be descriptive about the transgression.

Additional context
From ualbertalib/discovery#1591 (comment)

Danger has errored

[!] Invalid Dangerfile file: invalid byte sequence in UTF-8

 #  from Dangerfile:2
 #  -------------------------------------------
 #  # Make sure non-trivial amounts of code changes come with corresponding tests
 >  has_app_changes = !git.modified_files.grep(/lib\|app/).empty?
 #  has_spec_changes = !git.modified_files.grep(/spec/).empty?
 #  -------------------------------------------