fix durations not being cloned properly

``moment.duration`` does not return an equivalent Duration for all
inputs.  Add a test for this and fix the issue by reusing the
Duration's constructor argument.
fixing failing dst tests
bubbling up values on durations when adding or subtracting
Merge pull request #863 from frasertweedale/bugfix/clone-duration

fix durations not being cloned properly
Adding Persian Support
grunt is enough

There was not test task, `grunt` is enough for testing. In fact this was misleading for me
Merge pull request #871 from ebraminio/patch-1

grunt is enough
Merge pull request #870 from ebraminio/develop

Adding Persian Support
Added tests for Albanian, see #872
Merge pull request #876 from Oire/feature/albanian-tests

Added tests for Albanian
adding note on minified language files
Merge branch 'develop' of github.com:timrwood/moment into develop

* 'develop' of github.com:timrwood/moment:
  Added tests for Albanian, see #872
Don't test JSON.stringify if it doesn't exist #867
2.1.0 release