CI: only trigger jobs when relevant changes occur

.gitlab-ci.yml

@@ -10,6 +10,11 @@ stages:
   - deploy
 
 build:
+  only:
+    changes:
+      - src/**
+      - demo/**
+      - compile.sh
   stage: build
   script:
    - bash ./compile.sh
@@ -23,8 +28,13 @@ build:
       - css/theme/stereopticon.css
 
 pages:
-  only: 
-    - master
+  only:
+    changes:
+      - src/**
+      - demo/**
+      - compile.sh
+    refs:
+      - master
   dependencies: 
     - build
   stage: deploy