index: add `listSecrets` method

lib/index.js

@@ -312,6 +312,16 @@ export default class Now extends EventEmitter {
     uploadChunk();
   }
 
+  async listSecrets () {
+    return this.retry(async (bail, attempt) => {
+      if (this._debug) console.time(`> [debug] #${attempt} GET /secrets`);
+      const res = await this._fetch('/now/secrets');
+      if (this._debug) console.timeEnd(`> [debug] #${attempt} GET /secrets`);
+      const body = await res.json();
+      return body.secrets;
+    });
+  }
+
   async list (app) {
     const query = app ? `?app=${encodeURIComponent(app)}` : '';