Fix allocating Buffer in early commit (#22379)

Summary:
Commit d9c2cdae41 brings compatibility with Node 10, but replaced allocating buffer incorrectly.
dulmandakh made two comments and shows how to do it based on NodeJS documentation https://nodejs.org/api/buffer.html#buffer_new_buffer_size

This PR just fixes that commit.
Pull Request resolved: https://github.com/facebook/react-native/pull/22379

Differential Revision: D13166867

Pulled By: hramos

fbshipit-source-id: 207528739889c044021a4b97ef94c33d56de3e89

local-cli/generator/promptSync.js

@@ -43,7 +43,7 @@ function create() {
       process.stdin.setRawMode(true);
     }
 
-    var buf = Buffer.from(3);
+    var buf = Buffer.alloc(3);
     var str = '',
       character,
       read;
@@ -62,7 +62,7 @@ function create() {
           insert = str.length;
           process.stdout.write('\u001b[2K\u001b[0G' + ask + str);
           process.stdout.write('\u001b[' + (insert + ask.length + 1) + 'G');
-          buf = Buffer.from(3);
+          buf = Buffer.alloc(3);
         }
         continue; // any other 3 character sequence is ignored
       }