Upgrade rust/crates/regex to 1.5.4

Test: make
Change-Id: I0eab39246dc2aea41a62c15661e350b490f06c1d
diff --git a/src/backtrack.rs b/src/backtrack.rs
index 6100c17..a3d25d6 100644
--- a/src/backtrack.rs
+++ b/src/backtrack.rs
@@ -16,10 +16,10 @@
 // the bitset has to be zeroed on each execution, which becomes quite expensive
 // on large bitsets.
 
-use exec::ProgramCache;
-use input::{Input, InputAt};
-use prog::{InstPtr, Program};
-use re_trait::Slot;
+use crate::exec::ProgramCache;
+use crate::input::{Input, InputAt};
+use crate::prog::{InstPtr, Program};
+use crate::re_trait::Slot;
 
 type Bits = u32;
 
@@ -196,7 +196,7 @@
     }
 
     fn step(&mut self, mut ip: InstPtr, mut at: InputAt) -> bool {
-        use prog::Inst::*;
+        use crate::prog::Inst::*;
         loop {
             // This loop is an optimization to avoid constantly pushing/popping
             // from the stack. Namely, if we're pushing a job only to run it