Merge pull request #4812 from mozilla/pyup-update-pytest-variables-1.5.0-to-1.5.1

Update pytest-variables to 1.5.1

tests/ui/requirements.txt

@@ -4,6 +4,6 @@ PyPOM==1.1.1
 pytest==3.0.6
 pytest-instafail==0.3.0
 pytest-selenium==1.9.1
-pytest-variables==1.5.0
+pytest-variables==1.5.1
 pytest-xdist==1.15.0
 selenium==3.0.2