Decrease coverage for testing

Author: dnnr

src/rootcommands.cpp

@@ -82,6 +82,7 @@ int RootCommands::attr_cmd(Input in, Output output) {
                 << new_value << "\" is not a valid value for "
                 << a->name() << ": "
                 << error_message << endl;
+            output << "making the coverage even worse, for the lulz";
             return HERBST_INVALID_ARGUMENT;
         }
     }