Bump pygments from 2.2.0 to 2.7.4 in /tests (#25)

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]>

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

Author: dependabot[bot]

tests/requirements.txt

@@ -5,7 +5,7 @@ isort==4.3.20
 pdfminer.six==20170419
 pycodestyle==2.3.1
 pyflakes==1.5.0
-Pygments==2.2.0
+Pygments==2.7.4
 pytest==3.0.7
 pytest-cov==2.5.0
 pytest-isort==0.1.0