Add yarn to npm run upgrade

scripts/upgrade.sh

@@ -13,6 +13,11 @@ if [[ $(npm --version) < $npmMinVersion ]]; then
   exit 0
 fi
 
+if ! which yarn > /dev/null; then
+  echo 'You need yarn'
+  exit 0
+fi
+
 if pgrep peertube > /dev/null; then
   echo 'PeerTube is running!'
   exit 0
@@ -20,9 +25,9 @@ fi
 
 git pull origin $(git rev-parse --abbrev-ref HEAD) || exit -1
 
-npm install
-npm update
-cd client && npm update && cd ../
+yarn install
+yarn update
+cd client && yarn update && cd ../
 npm run build
 
 echo "\n\nUpgrade finished! You can restart PeerTube that may run the migration scripts."