Update SublimePHPCoverage.py

Bug:
On windows, the file path comparison returns false even when the files are exactly the same.
I narrowed the issue down to mismatching / and \ characters 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, *nix machines do not have this issue.

The Fix:
The paths are now normalised first before comparison.