Fix factory_boy version, got lost in rebase.

requirements-dev.txt

 -r requirements.txt
 
 django-debug-toolbar==2.0
-factory_boy==2.9.2
+factory_boy==2.12
 Faker==1.0.8  # Pinning to avoid API changes to pydecimal in 0.x - could go higher in future
 flake8==3.7.9
 responses==0.10.6