add user-agent to all outgoing requests

lib/index.js

@@ -1,6 +1,7 @@
 import bytes from 'bytes';
 import chalk from 'chalk';
 import getFiles from './get-files';
+import ua from './ua';
 import hash from './hash';
 import retry from 'async-retry';
 import Agent from './agent';
@@ -280,6 +281,7 @@ export default class Now extends EventEmitter {
   _fetch (_url, opts = {}) {
     opts.headers = opts.headers || {};
     opts.headers.authorization = `Bearer ${this._token}`;
+    opts.headers['user-agent'] = ua;
     return this._agent.fetch(_url, opts);
   }
 }

lib/ua.js

@@ -0,0 +1,4 @@
+import os from 'os';
+import { version } from '../package';
+
+export default `now ${version} node-${process.version} ${os.platform()} (${os.arch()})`;