Stylua formatting (#785)

Uses Stylua to format all existing Lua files, and adds a CI check in
`lint` to pin this improvement. Excludes formatting dependencies, of
course.

plugin/src/init.server.lua

@@ -17,7 +17,7 @@ Log.setLogLevelThunk(function()
 end)
 
 local app = Roact.createElement(App, {
-	plugin = plugin
+	plugin = plugin,
 })
 local tree = Roact.mount(app, game:GetService("CoreGui"), "Rojo UI")