ligo-gracedb.spec: use python-srpm-macros

easy to resolve dependencies when building a src.rpm
11 jobs for add-missing-dependencies in 4 minutes and 2 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Build
passed #391534
build:debian:jessie

00:03:09

passed #391535
build:debian:stretch

00:01:14

passed #391533
build:el7

00:00:57

passed #391532
build:tarball

00:00:19

 
  Test
passed #391541
docs

00:00:51

passed #391542
syntax

00:00:41

passed #391536
test:python2.7

00:00:38

passed #391537
test:python3.4

00:00:45

passed #391538
test:python3.5

00:00:44

passed #391539
test:python3.6

00:00:45

passed #391540
test:python3.7

00:00:35