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] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -1,5 +1,5 @@
 Flask
-Pygments==1.6
+Pygments==2.7.4
 beautifulsoup4==4.3.2
 blinker==1.3
 docutils==0.11