Bug 1270801 - Update mock from 1.3.0 to 2.0.0

https://github.com/testing-cabal/mock/blob/master/NEWS
https://github.com/testing-cabal/mock/compare/1.3.0...2.0.0

requirements/dev.txt

@@ -8,7 +8,7 @@ datadiff==2.0.0 --hash=sha256:54049440a896de5247ee2e7b7aa5425f939ac832c37edb2101
 
 WebTest==2.0.21 --hash=sha256:223d26edb416718961ac503dd6cf97832321138dbe2e45127e3c24d503e83ba7
 
-mock==1.3.0 --hash=sha256:3f573a18be94de886d1191f27c168427ef693e8dcfcecf95b170577b2eb69cbb
+mock==2.0.0 --hash=sha256:5ce3c71c5545b472da17b72268978914d0252980348636840bd34a00b5cc96c1
 
 responses==0.5.1 --hash=sha256:3a907f7aae2fd2286d06cfdf238957786c38bbcadc451adceecc769a4ef882b7