1.21.0

• fix source nawma_sa_gov_au
• add source scambs_gov_uk (thanks @dt215git)
• add source peterborough_gov_uk (thanks @skipishere)
• add source kuringgai_nsw_gov_au (thanks @dt215git)
• add source environmentfirst_co_uk (thanks @dt215git)
• add source belmont_wa_gov_au (thanks @robbo600)
• return date instead of datetime for banyule_vic_gov_au (thanks @ravngr)
• test_sources.py: test if source returns invalid date format
• add source cheshire_east_gov_uk (thanks @greghesp)