Tests fail "spawnFailure" task on windows

[johnhunter]

Tests for grunt-casper fail on the "spawnFailure" task when run on windows.

Steps to reproduce:

1. Clone the repo
2. run npm install
3. run grunt

Expected:

All tests pass

Actual:

Running "spawnFailure" task
has 3 failed tests as the package attr of the testsuite node in the xml report contains an os specific absolute path. E.g. d:\projects\grunt-casper\test\fixtures\testFail where the expected value is test/fixtures/testFail