Make pygments part of 'testing' extras

Tests in test_terminalwriter depend on pygments being installed
to work, so it should be installed with the `testing` extras.

Author: nicoddemus

setup.cfg

@@ -70,6 +70,7 @@ testing =
     hypothesis>=3.56
     mock
     nose
+    pygments>=2.7.2
     requests
     xmlschema
 

tox.ini

@@ -47,7 +47,6 @@ deps =
     numpy: numpy>=1.19.4
     pexpect: pexpect>=4.8.0
     pluggymain: pluggy @ git+https://github.com/pytest-dev/pluggy.git
-    pygments>=2.7.2
     unittestextras: twisted
     unittestextras: asynctest
     xdist: pytest-xdist>=2.1.0