Fix spelling errors

Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>

src/modules/sni/tray.cpp

@@ -35,7 +35,7 @@ void Tray::onRemove(std::unique_ptr<Item>& item) {
 }
 
 auto Tray::update() -> void {
-  // Show tray only when items are availale
+  // Show tray only when items are available
   box_.set_visible(!box_.get_children().empty());
   // Call parent update
   AModule::update();