Rename CONTRIBUTIONS.md

(Gitlab wants it to be called CONTRIBUTING.md)
2 jobs for master in 4 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
failed #107022
test

00:00:04

 
  Deploy
skipped #107023
pages
 
Name Stage Failure
failed
test Test
warning: current Git remote contains credentials
Error downloading object: gwinc/test/A+.pkl (6ec7119): Smudge error: Error downloading gwinc/test/A+.pkl (6ec7119694e3a92be24a62b572e494b12ea8c4f14a21279c6dec95b9adf4cb87): batch response: Authentication required: Authorization error: https://gitlab-ci-token:jYwDx5eQyNikgMKWih9x@git.ligo.org/gwinc/pygwinc.git/info/lfs/objects/batch
Check that you have proper access to the repository

Errors logged to /builds/gwinc/pygwinc/.git/lfs/objects/logs/20180626T185413.876975329.log
Use `git lfs logs last` to view the log.
error: external filter 'git-lfs filter-process' failed
fatal: gwinc/test/A+.pkl: smudge filter lfs failed
ERROR: Job failed: exit code 1