Update yamale from 1.10.1 to 2.0

Author: pyup-bot

requirements/testing.txt

@@ -22,7 +22,7 @@ execnet==1.7.1
 # (Pinned to 4.4.2 since what we need for testing is still useful)
 Mercurial==4.4.2  # pyup: ignore
 
-yamale==1.10.1
+yamale==2.0
 pytest-mock==1.10.4
 
 # local debugging tools