Update lint group names

Fixes usage on a nightly after rust-lang/rust#50620

Author: killercup

cargo-fix/src/main.rs

@@ -197,7 +197,7 @@ fn rustfix_crate(rustc: &Path, filename: &str) -> Result<FixedCrate, Error> {
             .iter()
             .all(|s| s.file_name == file_name && s.line_range == range)
         {
-            trace!("rejecting as it spans mutliple files {:?}", suggestion);
+            trace!("rejecting as it spans multiple files {:?}", suggestion);
             continue;
         }
 

cargo-fix/tests/all/edition_upgrade.rs

@@ -131,7 +131,7 @@ fn upgrade_extern_crate() {
         .file(
             "src/lib.rs",
             r#"
-                #![warn(rust_2018_migration)]
+                #![warn(rust_2018_idioms)]
 
                 extern crate bar;