Rename 'npm run upgrade' to 'npm run upgrade-peertube'

It was confusing with the command 'npm run update'

README.md

@@ -178,7 +178,7 @@ You can check the application (CORS headers, tracker websocket...) by running:
 The following commands will upgrade the source (according to your current branch), upgrade node modules and rebuild client application:
 
     # systemctl stop peertube
-    $ npm run upgrade
+    $ npm run upgrade-peertube
     # systemctl start peertube
 
 ### Development

package.json

@@ -34,7 +34,8 @@
     "dev:client": "scripty",
     "start": "node dist/server",
     "check": "ts-node ./scripts/check.ts",
-    "upgrade": "scripty",
+    "upgrade-peertube": "scripty",
+    "upgrade": "echo 'This command was renamed to upgrade-peertube.'",
     "update-host": "ts-node ./scripts/update-host.ts",
     "test": "scripty",
     "help": "scripty",