Upgrade rust/crates/regex-syntax to 0.6.20

Test: make
Change-Id: If42f1186cfdfae7f6752ca48aa7501c7626459a6
diff --git a/METADATA b/METADATA
index 3aa3b91..70c34e5 100644
--- a/METADATA
+++ b/METADATA
@@ -7,13 +7,13 @@
   }
   url {
     type: ARCHIVE
-    value: "https://static.crates.io/crates/regex-syntax/regex-syntax-0.6.18.crate"
+    value: "https://static.crates.io/crates/regex-syntax/regex-syntax-0.6.20.crate"
   }
-  version: "0.6.18"
+  version: "0.6.20"
   license_type: NOTICE
   last_upgrade_date {
     year: 2020
-    month: 5
-    day: 28
+    month: 10
+    day: 26
   }
 }