ES6/ES2015/Babel + Webpack compatibility (#65)

Solve a transpiling issue with Babel where it may be evaluated in contexts with no global `this` defined.

lib/encoding.js

@@ -1,19 +1,19 @@
 // This is free and unencumbered software released into the public domain.
 // See LICENSE.md for more information.
 
-// If we're in node require encoding-indexes and attach it to the global.
 /**
  * @fileoverview Global |this| required for resolving indexes in node.
  * @suppress {globalThis}
  */
-if (typeof module !== "undefined" && module.exports &&
-    !this["encoding-indexes"]) {
-    require("./encoding-indexes.js");
-}
-
 (function(global) {
   'use strict';
 
+  // If we're in node require encoding-indexes and attach it to the global.
+  if (typeof module !== "undefined" && module.exports &&
+    !global["encoding-indexes"]) {
+    global['encoding-indexes'] = require("./encoding-indexes.js");
+  }
+
   //
   // Utilities
   //
@@ -3306,4 +3306,7 @@ if (typeof module !== "undefined" && module.exports &&
       EncodingIndexes: global["encoding-indexes"]
     };
   }
-}(this));
+
+// For strict environments where `this` inside the global scope
+// is `undefined`, take a pure object instead
+}(this || {}));