Added AutoIt

Language website: http://autoitscript.com
Example project on GitHub: https://github.com/jvanegmond/au3-minecraft-monitor

lib/linguist/languages.yml

@@ -122,6 +122,15 @@ AutoHotkey:
   - ahk
   primary_extension: .ahk
   
+AutoIt:
+  type: programming
+  color: "#36699B"
+  aliases:
+  - au3
+  - AutoIt3
+  - AutoItScript
+  primary_extension: .au3
+
 Awk:
   type: programming
   lexer: Awk