Bump Tern SHA to fix a doc parsing bug

I recently stumbled upon a bug in Tern related to parsing JSdoc comments (see marijnh/tern#250) that caused it to throw an unhandled exception while editing JavaScript in Brackets. This unhandled exception caused JS code hints to stop working. Happily @marijnh was able to fix the bug with 91a696a04b8de5c04b7c9f288ab940bbda124d66. Updating the Tern submodule accordingly keeps the JS code hinter happy (for now).

CC @dangoor