Merge branch 'fix-go-versions' into 'master'

Test against go1.12

Closes #217

See merge request gitlab-org/gitlab-workhorse!390

.gitlab-ci.yml

@@ -24,6 +24,10 @@ test using go 1.10:
 test using go 1.11:
   <<: *test_definition
 
+test using go 1.12:
+  image: golang:1.12
+  <<: *test_definition
+
 test:release:
   only:
     - tags