setup.py: parse version from version.py don't import

its simpler to parse the version number from `ligo.gracedb.version`, rather than importing, so that `six` isn't required on the build machine _before_ building. importing in setup.py has also been seen to confuse some coverage parsers, and other profiling tools.
6 jobs for parse-version in 3 minutes and 29 seconds (queued for 1 second)
Status Job ID Name Coverage
  Build
passed #134445
build:debian:jessie

00:03:10

passed #134446
build:debian:stretch

00:01:24

passed #134444
build:el7

00:00:58

passed #134443
build:tarball

00:00:26

 
  Test
passed #134447
test:python2.7

00:00:17

passed #134448
test:python3.6

00:00:18