fix(update): fix typo in stop error handling (#306)

no issue
- changed Nu to No, I guess this is a typo, if not feel free do close

lib/commands/update.js

@@ -64,7 +64,7 @@ class UpdateCommand extends Command {
             skip: (ctx) => !ctx.instance.running,
             task: () => {
                 return this.runCommand(StopCommand, {quiet: true}).catch((error) => {
-                    if (!(error instanceof errors.SystemError) || !error.message.match(/Nu running Ghost instance/)) {
+                    if (!(error instanceof errors.SystemError) || !error.message.match(/No running Ghost instance/)) {
                         return Promise.reject(error);
                     }
                 });