Revert "change PEP-440 version identifier to one that's actually accepted by pip/setuptools"

This reverts commit 8929e0dd00cccf0ca1891c008d0b4b327c1b25b2.
Revert "fix version identifier to comply with PEP 440"

This reverts commit 8f142d263912e90a091f12b26691762c67f031bf.