Clean up E0452 explanation

GuillaumeGomez · GuillaumeGomez · commit 19e69359564c · 2020-03-23T12:40:14.000+01:00
diff --git a/src/librustc_error_codes/error_codes/E0452.md b/src/librustc_error_codes/error_codes/E0452.md
@@ -1,4 +1,6 @@
-An invalid lint attribute has been given. Erroneous code example:
+An invalid lint attribute has been given.
+
+Erroneous code example:
 
 ```compile_fail,E0452
 #![allow(foo = "")] // error: malformed lint attribute
