Bump pygments from 2.1.3 to 2.7.4 (#72)

Bumps [pygments](https://github.com/pygments/pygments) from 2.1.3 to 2.7.4.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.1.3...2.7.4)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -1,4 +1,4 @@
 mkdocs==0.16.1
 mkdocs-material==1.0.2
-Pygments==2.1.3
+Pygments==2.7.4
 pymdown-extensions==1.6.1