Update requirements_dev.txt

Lets try to pin pytest mock before the breaking change.. The tests still needs to fixed as mocker patch dont really work.

Author: Hellowlol

requirements_dev.txt

@@ -8,7 +8,7 @@ pillow
 pytest
 pytest-cache
 pytest-cov
-pytest-mock
+pytest-mock<=1.11.2
 recommonmark
 requests
 sphinx