fix again bad string. use heredoc

Author: marcel corso

spec/call_spec.rb

@@ -39,7 +39,7 @@
     expect(voice_client)
       .to receive(:request)
       .with(:post, 'calls', { source: source, destination: destination, callFlow: call_flow.to_json })
-      .and_return("{'data':[{'id':'#{call_id}','status':'queued','source':'#{source}','destination':'#{destination}','createdAt':'2019-10-11T13:02:19Z','updatedAt':'2019-10-11T13:02:19Z','endedAt':null}],'_links':{'self':'/calls/#{call_id}'},'pagination':{'total_count':0,'pageCount':0,'currentPage':0,'perPage':0}}")
+      .and_return(%Q({"data":[{"id":"#{call_id}","status":"queued","source":"#{source}","destination":"#{destination}","createdAt":"2019-10-11T13:02:19Z","updatedAt":"2019-10-11T13:02:19Z","endedAt":null}],"_links":{"self":"/calls/#{call_id}"},"pagination":{"total_count":0,"pageCount":0,"currentPage":0,"perPage":0}}))
     call = client.call_create(source, destination, call_flow)
     expect(call.id).to eq call_id
   end