fix(Shard): erroneously returning false

The node documentation fails to correctly document when the backlog of unsent messages exceeds a certain threshhold the function will return false. This does not mean it will refuse to send- simply that it will take time. Issue in point: nodejs/node#7657 (comment)

src/sharding/Shard.js

@@ -140,10 +140,9 @@ class Shard extends EventEmitter {
    */
   send(message) {
     return new Promise((resolve, reject) => {
-      const sent = this.process.send(message, err => {
+      this.process.send(message, err => {
         if (err) reject(err); else resolve(this);
       });
-      if (!sent) throw new Error('SHARDING_CHILD_CONNECTION');
     });
   }