Merge make-bat-path-fix-7542: Fix path error in Sphinx make.bat file.

Author: amattjones
Reviewers: khorn
Fixes: #7542

This fixes a bad path that was preset in the make.bat file used for
building Sphinx docs.  The docs can now be built on Windows using this
file.

git-svn-id: svn://svn.twistedmatrix.com/svn/Twisted/trunk@43043 bbbe8e31-12d6-0310-92fd-ac37d47ddeeb