Upgrade pants to 1.1.0-rc7.
Upgrade pants to 1.1.0-rc7.

This helps test the pants release candidate to pave our way to upgrade to
the 1.1.0 release upgrade and it now limits our backends to python-only
for real. This means ivy is no longer bootstrapped to run python tests
for example.

Reviewed at https://reviews.apache.org/r/49872/

thinker0/aurora,medallia/aurora,apache/aurora,medallia/aurora,apache/aurora,crashlytics/aurora,rdelval/aurora,rdelval/aurora,rdelval/aurora,medallia/aurora,crashlytics/aurora,apache/aurora,rdelval/aurora,medallia/aurora,thinker0/aurora,medallia/aurora,thinker0/aurora,apache/aurora,apache/aurora,rdelval/aurora,thinker0/aurora,crashlytics/aurora,medallia/aurora,thinker0/aurora,rdelval/aurora,apache/aurora,crashlytics/aurora,crashlytics/aurora,thinker0/aurora,crashlytics/aurora