formating: upgrade to black 20.8b1
This required a couple of small tweaks to un-confuse black, but now it
works. Big formatting changes come from:
* Dramatically improved collection-splitting logic upstream
* Black having a strong (correct IMO) opinion that """ is better than '''
Differential Revision: https://phab.mercurial-scm.org/D9430
$ hg init
$ touch a
$ unset HGUSER
$ echo "[ui]" >> .hg/hgrc
$ echo "username= foo" >> .hg/hgrc
$ echo " bar1" >> .hg/hgrc
$ hg ci -Am m
adding a
abort: username 'foo\nbar1' contains a newline
[255]
$ rm .hg/hgrc
$ HGUSER=`(echo foo; echo bar2)` hg ci -Am m
adding a
abort: username 'foo\nbar2' contains a newline
[255]
$ hg ci -Am m -u "`(echo foo; echo bar3)`"
adding a
transaction abort!
rollback completed
abort: username 'foo\nbar3' contains a newline
[255]