math/py-keras: Update 2.1.4 -> 2.1.5

Port changes:

• Change to DISTVERSION
• Minor comment change
• Add PYNUMPY to RUN_DEPENDS
• Sort RUN_DEPENDS
• Remove USE_PYTHON=concurrent (not needed)
• Group USExx
• Replace WWW with the https version

PR: 226451
Submitted by: Neel Chauhan <neel@neelc.org> (maintainer)