Improve black reporting through precommit

When running `pre-commit run`, black only shows a failure without
showing *why* which is annoying, especially with #51 allowing running
`pre-commit` via tox. It also makes looking at the pre-commit report
from github more frustrating than necessary.

Enable option for black to also print the diff it wants on failure,
makes handling that much more comfortable.

Also remove duplicate `flake8-docstrings` in the flake8 documentation,
and fix indentation of the list closing bracket.

.pre-commit-config.yaml

@@ -29,7 +29,7 @@ repos:
     rev: 21.12b0
     hooks:
     -   id: black
-        args: [--check]
+        args: [--check, --diff]
 -   repo: https://github.com/PyCQA/flake8
     rev: 4.0.1
     hooks:
@@ -40,10 +40,9 @@ repos:
             'flake8-bugbear',
             'flake8-sfs',
             'flake8-comprehensions',
-            'flake8-docstrings',
             'flake8-implicit-str-concat',
             'pydocstyle>=5.0.0',
-         ]
+        ]
 -   repo: https://github.com/asottile/blacken-docs
     rev: v1.12.0
     hooks:

tests/run_tests.sh

@@ -10,7 +10,7 @@ for code in RST??? ; do
     echo "======"
     for file in $code/*.py ; do
         echo "flake8 --select RST $file"
-        flake8 --select RST $file 2>&1 | grep ": $code "
+        flake8 --select RST $file 2| grep ": $code "
     done
     echo "Good, $code violations reported, as expected."
 done