git-node: auto amend metadata and open manual amend on request

This makes sure manual amend is started in case the user requested
that without the need to edit any intermediate files.

Refs: nodejs#425

lib/landing_session.js

@@ -197,16 +197,11 @@ class LandingSession extends Session {
     cli.separator('New Message');
     cli.log(message.trim());
     const takeMessage = await cli.prompt('Use this message?');
+    await runAsync('git', ['commit', '--amend', '-F', messageFile]);
     if (takeMessage) {
-      await runAsync('git', ['commit', '--amend', '-F', messageFile]);
       return true;
     }
-
-    // TODO: fire the configured git editor on that file
-    cli.log(`Please manually edit ${messageFile}, then run\n` +
-      `\`git commit --amend -F ${messageFile}\` ` +
-      'to finish amending the message');
-    process.exit(1);  // make it work with git rebase -x
+    await runAsync('git', ['commit', '--amend']);
   }
 
   async final() {