Use yarn over npm

package.json

@@ -5,9 +5,10 @@
   "main": "dist/src/electron.js",
   "scripts": {
     "start": "electron .",
-    "test": "npm run test-backend",
-    "build": "tsc && cd app && npm run build && cd ..",
-    "test-backend": "cd backend && npm run test && cd ..",
+    "test": "yarn run test-backend",
+    "install": "cd app; yarn install; cd ..",
+    "build": "tsc && cd app && yarn run build && cd ..",
+    "test-backend": "cd backend && yarn run test && cd ..",
     "prepare-release": "./prepare-release.sh",
     "package": "ts-node package.ts",
     "package-with-docker": "./package-with-docker.sh"