Error writing JUnit Xml File

[vermeeca]

On my machine (Windows 10, node 4.2.3) the Karma Junit reporter produced an invalid path for the Junit Xml file, and always failed for me.

A commit that fixed the issue for me and describes the error message in more detail can be found here:
https://github.com/vermeeca/karma-junit-reporter/tree/absolute_outputFile

Opening this issue for feedback before submitting a pull request.

[dignifiedquire]

Looks good to me, please make a PR :)

[vermeeca]

Done -- #84