Update EndOfFileLineFeedFixer to only support PHP files

Fixes #318
@keradus, no code was ever "blindly" copied from somewhere else. Different projects have different standards. I saw that the rest of the codebase used == for these checks and concluded that it would create no bugs or hit any edge cases.

There isn't a single scenario in this case where === would yield different results than ==. I am all for using === for consistency, but the rest of the code should be updated similarly to limit confusion.