Fix Analyzer#file_ignore failure when pattern.class == RegExp

How to reproduce:

1.  Create a new instance of analyzer: `analyzer = Analyzer.new('.')`
2.  Observe that `analyzer.file_ignore(%w[ ... ], /regexp-pattern/)`
    raises undefined method 'end_with?' error
3.  Observe that documentation for Analyzer#file_ignore states
    that it accepts regular expressions as pattern
Merge pull request #162 from 4r2r/fix-file-ignore-bug

Fix Analyzer#file_ignore failure when pattern.class == RegExp