Clean up E0370 explanation

Author: GuillaumeGomez

src/librustc_error_codes/error_codes/E0370.md

@@ -1,5 +1,7 @@
 The maximum value of an enum was reached, so it cannot be automatically
-set in the next enum value. Erroneous code example:
+set in the next enum value.
+
+Erroneous code example:
 
 ```compile_fail,E0370
 #[repr(i64)]