Don't generate yarn lockfile on upgrade

package.json

@@ -38,7 +38,7 @@
     "update-host": "ts-node ./scripts/update-host.ts",
     "test": "scripty",
     "help": "scripty",
-    "postinstall": "cd client && yarn install",
+    "postinstall": "cd client && yarn install --pure-lockfile",
     "tsc": "tsc",
     "nodemon": "nodemon",
     "ts-node": "ts-node",

scripts/upgrade.sh

@@ -25,9 +25,7 @@ fi
 
 git pull origin $(git rev-parse --abbrev-ref HEAD) || exit -1
 
-yarn install
-yarn upgrade
-cd client && yarn upgrade && cd ../
+yarn install --pure-lockfile
 npm run build
 
 echo "\n\nUpgrade finished! You can restart PeerTube that may run the migration scripts."