Merge branch 'ab-server-config-defaults' into 'master'

Fix error on missing `server` config section

See merge request gitlab-org/gitlab-monitor!87
2 jobs for v3.3.1 in 1 minute and 8 seconds (queued for 3 seconds)
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Status Job ID Name Coverage
  Test
passed #4125930
rspec

00:00:24

passed #4125931
rubocop

00:00:53