More neutral message

 + Some commands (like diff) have non-zero exit status even without error. This
 message is more neutral.

src/exec_cmd.ml

@@ -112,7 +112,7 @@ let display_result command status =
   match status with
   | 0 -> (* No problem, do nothing *) ()
   | _ -> (* Problem occur, report it *)
-    sprintf "Problem while running: '%s'\nExited with code: %i\n"
+    sprintf "Command '%s' exited with code: %i\n"
       command status
     |> Messages.warning
 ;;