Update SublimePHPCoverage.py

On windows, the file path comparisons on line 99 returns false even though the files are exactly the same.
I narrowed down to mismatching / and \ in the file paths.

For instance, a simple string comparison on windows like this "some/random/file" == "some/random\file" returns false.

As far as I know, this isn't a problem with *nix machines.

Paths are now normalised first before comparison.