scope_guard/modules: Rename scope_guard to ScopeGuard

Using pascal case for the class name keeps it more consistent with the
majority of the other class names.

src/modules/sni/watcher.cpp

@@ -31,7 +31,7 @@ Watcher::~Watcher() {
 
 void Watcher::busAcquired(const Glib::RefPtr<Gio::DBus::Connection>& conn, Glib::ustring name) {
   GError* error = nullptr;
-  waybar::util::scope_guard error_deleter([error]() {
+  waybar::util::ScopeGuard error_deleter([error]() {
     if (error) {
       g_error_free(error);
     }