CI: update to Go 1.16.1 (#2842)

diff --git a/WORKSPACE b/WORKSPACE
index 26e1f80..b9463e4 100644
--- a/WORKSPACE
+++ b/WORKSPACE
@@ -6,7 +6,7 @@
 
 go_rules_dependencies(is_rules_go = True)
 
-go_register_toolchains(version = "1.16")
+go_register_toolchains(version = "1.16.1")
 
 http_archive(
     name = "com_google_protobuf",