Merge pull request #51 from jimsch/master

Correct value to match spec

Author: jimsch

src/main/java/COSE/HeaderKeys.java

@@ -14,7 +14,7 @@
 public enum HeaderKeys {
     Algorithm(1),
     CONTENT_TYPE(3),
-    KID(2),
+    KID(4),
     IV(5),
     CriticalHeaders(2),
     CounterSignature(7),