Merge branch 'renovate/docker-golang-1.x' into 'master'

chore(dependency): Update golang Docker tag to v1.15

See merge request monstercat/api!4

Author: menzerath

.gitlab-ci.yml

@@ -2,15 +2,15 @@ stages:
   - test
 
 lint:
-  image: golang:1.14
+  image: golang:1.15
   stage: test
   before_script:
     - go get -u github.com/mgechev/revive
   script:
     - revive -formatter stylish -exclude ./vendor/... ./...
 
 test:
-  image: golang:1.14
+  image: golang:1.15
   stage: test
   script:
     - go test -mod=vendor -cover -v ./...