Add vim modeline to Lua files without .lua extension

To be correctly detected by GitHub's linguist.

Author: jirutka

.busted

@@ -1,3 +1,5 @@
+-- vim: set ft=lua:
+
 return {
   _all = {
     helper = 'spec/spec_helper'

.luacheckrc

@@ -1,2 +1,4 @@
+-- vim: set ft=lua:
+
 std = 'luajit'
 globals = { 'ngx' }

.luacov

@@ -1,3 +1,5 @@
+-- vim: set ft=lua:
+
 return {
 
   -- filename to store stats collected

config.ld

@@ -1,3 +1,5 @@
+-- vim: set ft=lua:
+
 project = 'ngx-oauth'
 title   = 'ngx-oauth docs'
 package = 'ngx-oauth'