requirements: Update pygments to 2.1.1

- Fixed Jython compatibility
- Fixed HTML formatter output with leading empty lines
- Added a mapping table for LaTeX encodings and added utf8
- Fixed image formatter font searching on Macs
- Fixed deepcopy-ing of Token instances
- Fixed Julia string interpolation
- Fixed statefulness of HttpLexer between get_tokens calls
- Many smaller fixes to various lexers

requirements.txt

@@ -1,6 +1,6 @@
 Jinja2==2.8.0
 MarkupSafe==0.23
-Pygments==2.1.1
+Pygments==2.1.2
 pyPEG2==2.15.2
 PyYAML==3.11
 colorama==0.3.6