Upgrade rust/crates/regex to 1.3.7

Test: None
Change-Id: I26e69e1c8997da756f5da7bbd70727375ccf1d5d
diff --git a/METADATA b/METADATA
index 26317f2..53b95fe 100644
--- a/METADATA
+++ b/METADATA
@@ -9,11 +9,11 @@
     type: GIT
     value: "https://github.com/rust-lang/regex"
   }
-  version: "1.3.6"
+  version: "1.3.7"
   license_type: NOTICE
   last_upgrade_date {
     year: 2020
-    month: 3
-    day: 31
+    month: 4
+    day: 17
   }
 }