Add pre-existing field parameter for template draft creation.

Author: Chris Paul

src/main/java/com/hellosign/sdk/resource/TemplateDraft.java

@@ -274,6 +274,10 @@ public Map<String, Serializable> getPostFields() throws HelloSignException {
 				fields.put("merge_fields", mergeFieldArray.toString());
 			}
 
+			if (hasUsePreexistingFields()) {
+			    fields.put(REQUEST_USE_PREEXISTING_FIELDS, true);
+			}
+
 			if (isTestMode()) {
 				fields.put(REQUEST_TEST_MODE, true);	
 			}

src/main/java/com/hellosign/sdk/resource/UnclaimedDraft.java

@@ -239,7 +239,7 @@ public Map<String, Serializable> getPostFields() throws HelloSignException {
 			map.put(REQUEST_HIDE_TEXT_TAGS, isHidingTextTags());
 		}
 		if (hasUsePreexistingFields()) {
-		    map.put(REQUEST_USE_PREDEFINED_FIELDS, isUsingPreexistingFields());
+		    map.put(REQUEST_USE_PREEXISTING_FIELDS, isUsingPreexistingFields());
 		}
 		return map;
 	}