test: Fix alt-implicit-copy-unique. rs=me

Author: pcwalton

src/test/run-pass/alt-implicit-copy-unique.rs

@@ -1,7 +1,7 @@
 fn main() {
     let x = ~{mut a: ~10, b: ~20};
     match x {
-      ~{a: ref mut a, b: ref mut b} => {
+      ~{a: ref mut a, b: ref b} => {
         assert **a == 10; (*x).a = ~30; assert **a == 30;
       }
     }