Don't force push to sympy_doc
Deploy the docs as part of the script phase in Travis

This has several advantages:

- If it fails, the build will fail.
- We do not need to rebuild the docs. They are already built from the test
that builds the docs.
- We do not arbitrarily only deploy when the first test in the matrix is
finished. The deploying is now tied to the docs building matrix.
Fix bash syntax in .travis.yml
Fix name of deploy script in .travis.yml
Merge pull request #8214 from asmeurer/travis-docs

Travis docs