Use `"now"` nampespace for `"engines"`

lib/index.js

@@ -71,7 +71,8 @@ export default class Now extends EventEmitter {
 
     this._files = hashes;
 
-    const engines = pkg['now-engines'];
+    const nowProperties = pkg.now || {};
+    const engines = nowProperties.engines;
 
     const deployment = await retry(async (bail) => {
       if (this._debug) console.time('> [debug] /now/create');