Bump pygments from 1.6 to 2.7.4

Bumps [pygments](https://github.com/pygments/pygments) from 1.6 to 2.7.4.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@1.6...2.7.4)

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -30,7 +30,7 @@ mock==1.0.1
 nose==1.3.4
 nose-htmloutput==0.5.0
 oauthlib==1.0.3
-Pygments==1.6
+Pygments==2.7.4
 pytz==2015.7
 PyYAML==3.11
 raven==5.10.2