Speed up spellcheck by using 4 threads

Author: facelessuser

tox.ini

@@ -30,7 +30,7 @@ extras = docs
 deps = pyspelling
 commands =
     {envpython} -m mkdocs build --config-file {toxinidir}/mkdocs.yml
-    {envpython} -m pyspelling --config {toxinidir}/.pyspelling.yml
+    {envpython} -m pyspelling -j 4 --config {toxinidir}/.pyspelling.yml
 
 [testenv:checklinks]
 extras = docs