Update checkstyle to 8.10

- fix issues detected
  - YANG custom registrator should be subject to checkstyle
  - fix Java 8 syntax related violations

Change-Id: I0fc52c6612a40d851fd9bc3bf019621776b1f92a
diff --git a/bucklets/yang.bucklet b/bucklets/yang.bucklet
index 7ef9b33..8d5d83f 100644
--- a/bucklets/yang.bucklet
+++ b/bucklets/yang.bucklet
@@ -67,7 +67,7 @@
           deps = deps + YANG_TOOLS,
           resources = [ ':' + schema ],
           resources_root = ".",
-          do_checkstyle = False,
+          do_checkstyle = True,
           do_javadocs = False,
         )
     else: