[release] pantsbuild.pants 1.15.0.dev1

[John Sirois]

The second weekly dev release for the 1.15.x series is now available on pypi.

As usual, the release notes are available here: www.pantsbuild.org/notes-master.html

Thanks to the contributors in this cycle:

      6 Danny McClanahan

      5 Stu Hood

      3 Ekaterina Tyurina

      2 Daniel Wagner-Hall

      1 Nora Howard

      1 John Sirois

      1 Chris Livingston