Fix syntax of gitlab-ci file

.gitlab-ci.yml

@@ -1,9 +1,11 @@
-image: "ruby:2.5"
+stages:
+    - build
+    - stamp
 
 before_script:
     - apt-get -qq update && apt-get -qq install -y graphicsmagick rsync
 
-build:
+build-textures:
     stage: build
     script:
         - "./export.sh"
@@ -13,8 +15,9 @@ build:
             - "build/"
 
 stamp:
-    only: tags
     stage: stamp
+    only:
+        - tags
     script:
         - "./stamp.sh ${CI_COMMIT_TAG}"
 
@@ -22,4 +25,4 @@ stamp:
         paths:
             - "build/"
     dependencies:
-        - build
+        - build-textures