Fix a typo in usage example (#806)

Author: theswedishdev

docs/usage.asciidoc

@@ -66,7 +66,7 @@ When using the callback style API, the function will also return an object that
 [source,js]
 ----
 // calback API
-const requesty = client.search({
+const request = client.search({
   index: 'my-index',
   body: { foo: 'bar' }
 }, {
@@ -302,4 +302,4 @@ export interface ResurrectEvent {
   isAlive: boolean;
   connection: Connection;
 }
-----
+----