Fix environment issues for tests

Currently the tests for this task are very sensitive to environment and will always fail on Windows systems.

The tests for banner stripper have hard coded `\n` line endings, this means that Windows users who have not set their git global configuration to use UNIX line endings will see these tests fail.

On the other hand, Windows developers who *have* set their git global configuration for force UNIX style line endings will see the concatenation tests fail because the task uses `grunt.util.linefeed` for line endings, which defaults to `\r\n` on Windows systems. This means that the concatenated files will not match the LF-only fixtures pulled from the repo.

**My suggestion:**

* Include a .gitattributes file with `* eol=lf` to force git to save pulled text files with UNIX style line endings.
* Set `grunt.util.linefeed = '\n'` in the project's Gruntfile to override the default value in Windows environments.
* **Optional:** Change the banner stripper tests to use `grunt.util.linefeed` instead of hard coded `\n` characters.

What are your thoughts?