Update UI test

Author: GuillaumeGomez

src/test/ui/json-short.stderr

@@ -1,5 +1,6 @@
-{"message":"`main` function not found in crate `json_short`","code":{"code":"E0601","explanation":"No `main` function was found in a binary crate. To fix this error, add a
-`main` function. For example:
+{"message":"`main` function not found in crate `json_short`","code":{"code":"E0601","explanation":"No `main` function was found in a binary crate.
+
+To fix this error, add a `main` function:
 
 ```
 fn main() {