Bump pygments from 2.4.2 to 2.7.4 in /docs

Bumps [pygments](https://github.com/pygments/pygments) from 2.4.2 to 2.7.4.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](https://github.com/pygments/pygments/compare/2.4.2...2.7.4)

Signed-off-by: dependabot[bot] <support@github.com>

docs/requirements.txt

@@ -5,34 +5,69 @@
 #    pip-compile requirements.in
 #
 -e git+https://github.com/40ants/pygments-cl-repl.git#egg=pygments-cl-repl
+    # via
+    #   -r requirements.in
+    #   sphinxcontrib-cldomain
 -e git+https://github.com/40ants/sphinxcontrib-cldomain.git#egg=sphinxcontrib-cldomain
-alabaster==0.7.12         # via sphinx
-attrs==19.1.0             # via packaging
-babel==2.7.0              # via sphinx
-certifi==2019.6.16        # via requests
-chardet==3.0.4            # via requests
-docutils==0.15.2          # via sphinx
+    # via -r requirements.in
+alabaster==0.7.12
+    # via sphinx
+attrs==19.1.0
+    # via packaging
+babel==2.7.0
+    # via sphinx
+certifi==2019.6.16
+    # via requests
+chardet==3.0.4
+    # via requests
+docutils==0.15.2
+    # via sphinx
 future==0.17.1
-idna==2.8                 # via requests
-imagesize==1.1.0          # via sphinx
-jinja2==2.10.1            # via sphinx
-markupsafe==1.1.1         # via jinja2
-packaging==19.1           # via sphinx
-pygments==2.4.2           # via sphinx
-pyparsing==2.4.2          # via packaging
-pytz==2019.2              # via babel
-requests==2.22.0          # via sphinx
-six==1.12.0               # via packaging
-snowballstemmer==1.9.0    # via sphinx
+    # via sphinxcontrib-cldomain
+idna==2.8
+    # via requests
+imagesize==1.1.0
+    # via sphinx
+jinja2==2.10.1
+    # via sphinx
+markupsafe==1.1.1
+    # via jinja2
+packaging==19.1
+    # via sphinx
+pygments==2.7.4
+    # via
+    #   pygments-cl-repl
+    #   sphinx
+pyparsing==2.4.2
+    # via packaging
+pytz==2019.2
+    # via babel
+requests==2.22.0
+    # via sphinx
+six==1.12.0
+    # via packaging
+snowballstemmer==1.9.0
+    # via sphinx
 sphinx-bootstrap-theme==0.7.1
+    # via -r requirements.in
 sphinx==2.2.0
-sphinxcontrib-applehelp==1.0.1  # via sphinx
-sphinxcontrib-devhelp==1.0.1  # via sphinx
-sphinxcontrib-htmlhelp==1.0.2  # via sphinx
-sphinxcontrib-jsmath==1.0.1  # via sphinx
-sphinxcontrib-qthelp==1.0.2  # via sphinx
-sphinxcontrib-serializinghtml==1.1.3  # via sphinx
-urllib3==1.25.3           # via requests
+    # via
+    #   -r requirements.in
+    #   sphinxcontrib-cldomain
+sphinxcontrib-applehelp==1.0.1
+    # via sphinx
+sphinxcontrib-devhelp==1.0.1
+    # via sphinx
+sphinxcontrib-htmlhelp==1.0.2
+    # via sphinx
+sphinxcontrib-jsmath==1.0.1
+    # via sphinx
+sphinxcontrib-qthelp==1.0.2
+    # via sphinx
+sphinxcontrib-serializinghtml==1.1.3
+    # via sphinx
+urllib3==1.25.3
+    # via requests
 
 # The following packages are considered to be unsafe in a requirements file:
-# setuptools==41.2.0        # via sphinx, sphinx-bootstrap-theme
+# setuptools