Upgrade rust/crates/regex to 1.5.4

Test: make
Change-Id: I0eab39246dc2aea41a62c15661e350b490f06c1d
diff --git a/src/literal/mod.rs b/src/literal/mod.rs
index 783c63b..980f523 100644
--- a/src/literal/mod.rs
+++ b/src/literal/mod.rs
@@ -6,7 +6,7 @@
 #[allow(missing_docs)]
 #[cfg(not(feature = "perf-literal"))]
 mod imp {
-    use syntax::hir::literal::Literals;
+    use regex_syntax::hir::literal::Literals;
 
     #[derive(Clone, Debug)]
     pub struct LiteralSearcher(());