Bump pygments from 2.2.0 to 2.7.4 in /requirements (#34)

Bumps [pygments](https://github.com/pygments/pygments) from 2.2.0 to 2.7.4.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.2.0...2.7.4)

Signed-off-by: dependabot[bot] <[email protected]>

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

Author: dependabot[bot]

requirements/dev.txt

@@ -1,6 +1,6 @@
 -r common.txt
 ForgeryPy==0.1
-Pygments==2.2.0
+Pygments==2.7.4
 colorama==0.3.9
 coverage==4.4.1
 httpie==1.0.3