Bump pygments from 2.6.1 to 2.7.4 in /doc/src/sphinx

Bumps [pygments](https://github.com/pygments/pygments) from 2.6.1 to 2.7.4.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.6.1...2.7.4)

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

Author: dependabot[bot]

doc/src/sphinx/Pipfile.lock

@@ -1,27 +1,27 @@
+-i https://pypi.org/simple/
 alabaster==0.7.12
-Babel==2.8.0
-certifi==2020.6.20
-chardet==3.0.4
+babel==2.9.0
+certifi==2020.12.5
+chardet==4.0.0
 commonmark==0.9.1
 docutils==0.16
 idna==2.10
 imagesize==1.2.0
-Jinja2==2.11.2
-MarkupSafe==1.1.1
-packaging==20.4
-Pygments==2.6.1
+jinja2==2.11.3
+markupsafe==1.1.1
+packaging==20.9
+pygments==2.7.4
 pyparsing==2.4.7
-pytz==2020.1
+pytz==2021.1
 recommonmark==0.6.0
-requests==2.24.0
-six==1.15.0
-snowballstemmer==2.0.0
-Sphinx==3.1.2
+requests==2.25.1
+snowballstemmer==2.1.0
 sphinx-rtd-theme==0.5.0
+sphinx==3.1.2
 sphinxcontrib-applehelp==1.0.2
 sphinxcontrib-devhelp==1.0.2
 sphinxcontrib-htmlhelp==1.0.3
 sphinxcontrib-jsmath==1.0.1
 sphinxcontrib-qthelp==1.0.3
 sphinxcontrib-serializinghtml==1.1.4
-urllib3==1.25.9
+urllib3==1.26.4