fix break in node 8

Author: calvinmetcalf

index.js

@@ -11,6 +11,10 @@ function CipherBase (hashMode) {
   } else {
     this.final = this._finalOrDigest
   }
+  if (this._final) {
+    this.__final = this._final
+    this._final = null
+  }
   this._decoder = null
   this._encoding = null
 }
@@ -59,15 +63,15 @@ CipherBase.prototype._transform = function (data, _, next) {
 CipherBase.prototype._flush = function (done) {
   var err
   try {
-    this.push(this._final())
+    this.push(this.__final())
   } catch (e) {
     err = e
   } finally {
     done(err)
   }
 }
 CipherBase.prototype._finalOrDigest = function (outputEnc) {
-  var outData = this._final() || new Buffer('')
+  var outData = this.__final() || new Buffer('')
   if (outputEnc) {
     outData = this._toString(outData, outputEnc, true)
   }