Upcoming version support changes

This version, Babel 2.9, is the last version of Babel to support Python 2.7, Python 3.4, and Python 3.5.

Improvements

CLDR: Use CLDR 37 – Aarni Koskela (#734)
Dates: Handle ZoneInfo objects in get_timezone_location, get_timezone_name - Alessio Bogon (#741)
Numbers: Add group_separator feature in number formatting - Abdullah Javed Nesar (#726)

Dates: Correct default Format().timedelta format to 'long' to mute deprecation warnings – Aarni Koskela
Import: Simplify iteration code in "import_cldr.py" – Felix Schwarz
Import: Stop using deprecated ElementTree methods "getchildren()" and "getiterator()" – Felix Schwarz
Messages: Fix unicode printing error on Python 2 without TTY. – Niklas Hambüchen
Messages: Introduce invariant that _invalid_pofile() takes unicode line. – Niklas Hambüchen
Tests: fix tests when using Python 3.9 – Felix Schwarz
Tests: Remove deprecated 'sudo: false' from Travis configuration – Jon Dufresne
Tests: Support Py.test 6.x – Aarni Koskela
Utilities: LazyProxy: Handle AttributeError in specified func – Nikiforov Konstantin (#724)
Utilities: Replace usage of parser.suite with ast.parse – Miro Hrončok