Use newer release of Pygments

 * Includes [Haskell types fix by @teh](https://bitbucket.org/birkenfeld/pygments-main/pull-requests/685/two-haskell-fixes/diff)
 * Local docs build then exhibit proper Haskell highlighting including type literals etc

 Fixes #359

Author: declension

doc/requirements.txt

@@ -10,7 +10,7 @@ Jinja2==2.8
 livereload==2.4.1
 MarkupSafe==0.23
 pathtools==0.1.2
-Pygments==2.1.1
+Pygments==2.2.0
 pytz==2015.7
 PyYAML==3.11
 recommonmark==0.4.0