Clean up E0642 explanation

GuillaumeGomez · GuillaumeGomez · commit c183c3f4d167 · 2020-06-04T13:03:50.000+02:00
diff --git a/src/librustc_error_codes/error_codes/E0642.md b/src/librustc_error_codes/error_codes/E0642.md
@@ -1,6 +1,6 @@
 Trait methods currently cannot take patterns as arguments.
 
-Example of erroneous code:
+Erroneous code example:
 
 ```compile_fail,E0642
 trait Foo {
