fix yml syntax

.gitlab-ci.yml

 image: $CI_REGISTRY/r3/docker/julia-custom
 
 stages:
-  - test
+  - test-v1.5
+  - test-v1.6
   - format-check
   - deploy-doc
 
@@ -27,14 +28,14 @@ variables:
 # --------------------------------------
 
 linux:v1.5:
-  stage: test
+  stage: test-v1.5
   variables:
     JULIA_VER: "v1.5.3"
   <<: *global_settings
   <<: *global_testing_linux
 
 windows10:v1.5:
-  stage: test
+  stage: test-v1.5
   tags:
     - windows10
   variables:
@@ -43,7 +44,7 @@ windows10:v1.5:
   <<: *global_testing_win
 
 windows8:v1.5:
-  stage: test
+  stage: test-v1.5
   tags:
     - windows8
   variables:
@@ -55,7 +56,7 @@ windows8:v1.5:
 # --------------------------------------
 
 linux:v1.6:
-  stage: test
+  stage: test-v1.6
   needs: ["linux:v1.5"]
   variables:
     JULIA_VER: "v1.6.0"
@@ -63,7 +64,7 @@ linux:v1.6:
   <<: *global_testing_linux
 
 windows10:v1.6:
-  stage: test
+  stage: test-v1.6
   needs: ["windows10:v1.5"]
   tags:
     - windows10
@@ -73,7 +74,7 @@ windows10:v1.6:
   <<: *global_testing_win
 
 windows8:v1.6:
-  stage: test
+  stage: test-v1.6
   needs: ["windows8:v1.5"]
   tags:
     - windows8
@@ -85,8 +86,8 @@ windows8:v1.6:
 # Test Docker run with Julia v1.6
 # --------------------------------------
 
-docker:v1.6.0:
-  stage: test
+docker:v1.6:
+  stage: test-v1.6
   rules:
     - if: $CI_PIPELINE_SOURCE == "external_pull_request_event"
     - if: $CI_COMMIT_BRANCH == "master"