Add AnswerCall Attribute To Ring BXML Verb

Added the answerCall attribute to the Ring class and updated the test to expect it in serialization output.

Author: abaldwin-Bandwidth

src/main/java/com/bandwidth/voice/bxml/verbs/Ring.java

@@ -19,4 +19,11 @@ public class Ring implements Verb {
      */
     @XmlAttribute
     private Double duration;
+
+    /**
+     * (optional) A boolean indicating whether or not to answer the call when Ring is executed on an unanswered
+     * incoming call. Default value is 'true'.
+     */
+    @XmlAttribute
+    private boolean answerCall;
 }

src/test/java/com/bandwidth/BxmlTest.java

@@ -429,14 +429,15 @@ public void testStopRecording() {
     @Test
     public void testRing() {
         Ring ring = Ring.builder()
-            .duration(3.0)
-            .build();
+                .duration(3.0)
+                .answerCall(false)
+                .build();
 
         String response = new Response()
             .add(ring)
             .toBXML();
 
-        String expected = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><Response><Ring duration=\"3.0\"/></Response>";
+        String expected = "<?xml version=\"1.0\" encoding=\"UTF-8\"?><Response><Ring duration=\"3.0\" answerCall=\"false\"/></Response>";
 
         assertEquals("BXML strings not equal", expected, response);
     }