Bump pytz from 2020.1 to 2020.4

Bumps pytz from 2020.1 to 2020.4.

Commits

• 513450f Drop unwanted and unecessary shebang line
• d6a6878 Generate fat datafiles
• c36aa69 Update assert to cope with database updates
• fb431f2 Bump version numbers to 2020.4/2020d
• 5c4a3c6 IANA 2020d
• a4a62d8 Squashed 'tz/' changes from 7aec41a1d..d828740bb
• 55e2d1c Update travis config to bionic environment
• 13b5005 Add python 3.7 and 3.8 to the compatibility list
• ea3336a [compat] Add python 3.7 and 3.8 to the compatibility list
• 616ca4a Allow skipping of startup resource checks
• Additional commits viewable in compare view