updated sympy sublodule
Added the condition of not sorting when keys of dict are instances of Symbol Fixes #37
now sorting the dictionary only once
Merge pull request #39 from sahilshekhawat/fix_satisfiable

Fix satisfiable (fixes #37)
Bump version to 21
Basic Travis-CI configuration
Update imports to make unittests work properly
Fix path to App Engine SDK
Install repo NumPy to speed up build
Have App Engine server skip update prompt
Make App Engine server start in background
Run PhantomJS tests on Travis
Change `sudo npm` to just `npm`