fix typo
Merge pull request #3228 from maximsch2/fix_parallel_docs_typo

Fix typo in IPython.Parallel documentation.
The HTML output type accidentally got removed from the OutputArea.

This commit adds it back at the approp. point in the
OutputArea.display_order.
Merge pull request #3229 from ellisonbg/htmloutput

The HTML output type accidentally got removed from the OutputArea.