Upgrade rust/crates/regex-syntax to 0.6.22

Test: make
Change-Id: I4979a9897fa2edeb552d795b067abcdd6036de0a
diff --git a/src/lib.rs b/src/lib.rs
index f35c913..edf1b99 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -155,6 +155,7 @@
 */
 
 #![deny(missing_docs)]
+#![warn(missing_debug_implementations)]
 #![forbid(unsafe_code)]
 
 pub use error::{Error, Result};