Moved cache generation into if clause

.gitlab-ci.yml

@@ -15,10 +15,13 @@ cache:
           - frontend/node_modules
 
 before_script:
-    - yarn install
+    - >
-    - cd frontend
+      if [ ! -d "node_modules" ]; then
-    - yarn install
+        yarn install
-    - cd ..
+        cd frontend
+        yarn install
+        cd ..
+      fi
 
 test_backend:
     stage: test