Fix for wrong separator in entry

[sergeioff]

This PR fixes the following problem:
When plugin is executed on Windows environment and entries contain path separator (e.g. entries: ['js/main.js']) it will lead to a mismatch between files and entries, because in entries the separator will be "/' and in files "".

[coveralls]

Pull Request Test Coverage Report for Build 44

• 4 of 4 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-2.5%) to 97.5%

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Totals
Change from base Build 37:	-2.5%
Covered Lines:	28
Relevant Lines:	28

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💛 - Coveralls

[der-On]

I'm not sure if the place to check for this is the correct one. Shouldn't this be handled by the bundle function instead? Also I'm not shure if browserify/watchify should deal with path seperators? Or maybe it is already the case in a later version of browserify?