Bump pygments from 2.5.2 to 2.7.4 in /docs (#15)

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

Author: dependabot[bot]

Diff for: docs/requirements.txt

@@ -9,7 +9,7 @@ jinja2==2.11.3
 jsonpointer==2.1
 markupsafe==1.1.1
 packaging==20.9
-pygments==2.5.2
+pygments==2.7.4
 pyparsing==2.4.7
 pytz==2021.3
 pyyaml==5.4.1