fix comma at end of enumerator list [-Wpedantic]

lib/nghttp2_int.h

@@ -51,7 +51,7 @@ typedef enum {
    * Invalid HTTP header field was received but it can be treated as
    * if it was not received because of compatibility reasons.
    */
-  NGHTTP2_ERR_IGN_HTTP_HEADER = -105,
+  NGHTTP2_ERR_IGN_HTTP_HEADER = -105
 } nghttp2_internal_error;
 
 #endif /* NGHTTP2_INT_H */