buildrpm: bump bundled docutils version to 0.14 when building for centos{5,6}

when building rpm packages for centos 5 and 6, we bundle a mercurial-specific
version of docutils in /opt/python-hg/lib/python2.7/site-packages/docutils

Let's bump the embedded docutils version from 0.12 (released in 2014) to
0.14 (latest as of today)

contrib/mercurial.spec

@@ -6,8 +6,8 b''
 
 %global pythonver %{withpython}
 %global pythonname Python-%{withpython}
-%global docutilsname docutils-0.12
-%global docutilsmd5 4622263b62c5c771c03502afa3157768
+%global docutilsname docutils-0.14
+%global docutilsmd5 c53768d63db3873b7d452833553469de
 %global pythonhg python-hg
 %global hgpyprefix /opt/%{pythonhg}
 # byte compilation will fail on some some Python /test/ files