Added test cases for superagent

Author: Napalys

javascript/ql/test/library-tests/frameworks/ClientRequests/tst.js

@@ -314,3 +314,9 @@ function usePolyfill() {
             return response.text()
         })
 }
+
+function useSuperagent(url){
+    superagent('GET', url); // Not flagged
+    superagent.del(url); // Not flagged
+    superagent.agent().post(url).send(data); // Not flagged
+}