Check .gitignore and .dockerignore

[andreoliwa]

Expected Behavior

Check ignore files like .gitignore and .dockerignore.

Current Behavior

They are not being checked.

Possible Solution

Use #165 to represent these ignore files, but #183 should be done first though.

This solution below is not valid anymore:

class IgnoreFile(BaseFile):
    pass
class GitIgnore(IgnoreFile):
    pass
class DockerIgnore(IgnoreFile):
    pass