New implementation of getCurrentBranch() to use "git rev-parse --abbrev-...

...ref HEAD"

The implementation of getCurrentBranch() using 'git status --porcelain --branch' didn't work for me.  Running the command in the terminal produced:

    git status --porcelain --branch                                    
    ## task/solr
    M composer.json
    ?? gulpfile.js

The method was ignoring the first line and returned the first letter of the line 2, 'M'.

I have modified this to use 'git rev-parse --abbrev-ref HEAD' which returns a single string.

Also - my first Open Source contribution!