Update to rustfmt-preview (#348)

* Update to rustfmt-preview.

* Run "cargo fmt --all" with rustfmt 0.4.1.

rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.

* Fix a long line that rustfmt 0.4.1 can't handle.

* Remove unneeded commas left behind by rustfmt.

lib/faerie/src/traps.rs

@@ -1,7 +1,7 @@
 //! Faerie trap manifests record every `TrapCode` that cretonne outputs during code generation,
 //! for every function in the module. This data may be useful at runtime.
 
-use cretonne_codegen::{ir, binemit};
+use cretonne_codegen::{binemit, ir};
 
 /// Record of the arguments cretonne passes to `TrapSink::trap`
 pub struct FaerieTrapSite {
@@ -23,7 +23,6 @@ pub struct FaerieTrapSink {
     pub sites: Vec<FaerieTrapSite>,
 }
 
-
 impl FaerieTrapSink {
     /// Create an empty `FaerieTrapSink`
     pub fn new(name: &str, code_size: u32) -> Self {