Update to the latest stable rustfmt, 0.4.2-stable (febbb36 2018-04-12).

lib/frontend/src/frontend.rs

@@ -607,7 +607,6 @@ where
 #[cfg(test)]
 mod tests {
 
-    use Variable;
     use cretonne_codegen::entity::EntityRef;
     use cretonne_codegen::ir::types::*;
     use cretonne_codegen::ir::{AbiParam, ExternalName, Function, InstBuilder, Signature};
@@ -615,6 +614,7 @@ mod tests {
     use cretonne_codegen::settings::CallConv;
     use cretonne_codegen::verifier::verify_function;
     use frontend::{FunctionBuilder, FunctionBuilderContext};
+    use Variable;
 
     fn sample_function(lazy_seal: bool) {
         let mut sig = Signature::new(CallConv::SystemV);