Normalize file paths before comparison (Update SublimePHPCoverage.py)

#### The 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.