fix: No need to format string with unused 'arg' named argument (#484)

The fmt::format() function looks for the "{arg}" named argument
in the given "format" string which does not exist. It will fail
if the string contains any {...} curled-brace substring.

Consequently, any "on-click*" option's command line containing for
instance substring like "${var}" or "awk '{...}'" will crash the program.

Signed-off-by: Thomas Venriès <thomas.venries@gmail.com>

src/AModule.cpp

@@ -46,7 +46,7 @@ bool AModule::handleToggle(GdkEventButton* const& e) {
     format = config_["on-click-forward"].asString();
   }
   if (!format.empty()) {
-    pid_.push_back(util::command::forkExec(fmt::format(format, fmt::arg("arg", click_param_))));
+    pid_.push_back(util::command::forkExec(format));
   }
   dp.emit();
   return true;