docs: Update plugin update guide to use RC (#371)

Author: jcesarmobile

docs/main/updating/plugins/7-0.md

@@ -32,7 +32,8 @@ From the plugin folder, run `npx @capacitor/plugin-migration-v6-to-v7@latest` an
 
 ### Updating package.json
 
-Update `@capacitor/cli`, `@capacitor/core`, `@capacitor/android` and `@capacitor/ios` to `next` version.
+Update `@capacitor/cli`, `@capacitor/core`, `@capacitor/android` and `@capacitor/ios` in devDependencies to `^7.0.0-rc.0` version.
+Update `@capacitor/core` in peerDependencies to `>=7.0.0-rc.0` version.
 
 ### Update Android Plugin Variables