[bug 1202288] Downgrade mock in requirements.txt
[bug 1202288] Downgrade mock in requirements.txt

lgp171188/fjord,Ritsyy/fjord,hoosteeno/fjord,Ritsyy/fjord,mozilla/fjord,lgp171188/fjord,Ritsyy/fjord,mozilla/fjord,lgp171188/fjord,hoosteeno/fjord,hoosteeno/fjord,hoosteeno/fjord,lgp171188/fjord,mozilla/fjord,mozilla/fjord,Ritsyy/fjord