chore: es6 base64 parser (#75)

Signed-off-by: Grant Timmerman <timmerman+devrel@google.com>

lib/formats/base64.js

@@ -1,15 +1,16 @@
+class Base64Parser {
+  constructor(decorator) {
+    this.decorator = decorator;
+  }
 
-function Parser(decorator) {
-  this.decorator = decorator;
-}
+  parse(payload) {
+    let payloadToParse = payload;
+    if (this.decorator) {
+      payloadToParse = this.decorator.parse(payload);
+    }
 
-Parser.prototype.parse = function(payload) {
-  let toparse = payload;
-  if (this.decorator) {
-    toparse = this.decorator.parse(payload);
+    return Buffer.from(payloadToParse, "base64").toString();
   }
+}
 
-  return Buffer.from(toparse, "base64").toString();
-};
-
-module.exports = Parser;
+module.exports = Base64Parser;