Add errorLoading translation of Thai language.

This closes https://github.com/select2/select2/pull/4521.

src/js/select2/i18n/th.js

@@ -1,6 +1,9 @@
 define(function () {
   // Thai
   return {
+    errorLoading: function () {
+      return 'ไม่สามารถค้นข้อมูลได้';
+    },
     inputTooLong: function (args) {
       var overChars = args.input.length - args.maximum;