Update slow buffer creation calls (#456)

lib/types.js

@@ -13,11 +13,7 @@
  */
 
 let utils = require('./utils'),
-    platform = require('./platform'),
-    buffer = require('buffer'); // For `SlowBuffer`.
-
-let Buffer = buffer.Buffer;
-let SlowBuffer = buffer.SlowBuffer;
+    platform = require('./platform');
 
 // Convenience imports.
 let Tap = utils.Tap;
@@ -32,7 +28,7 @@ let TYPES;
 let RANDOM = new utils.Lcg();
 
 // Encoding tap (shared for performance).
-let TAP = new Tap(new SlowBuffer(1024));
+let TAP = new Tap(Buffer.allocUnsafeSlow(1024));
 
 // Currently active logical type, used for name redirection.
 let LOGICAL_TYPE = null;
@@ -443,7 +439,7 @@ class Type {
 
   static __reset (size) {
     debug('resetting type buffer to %d', size);
-    TAP.buf = new SlowBuffer(size);
+    TAP.buf = Buffer.allocUnsafeSlow(size);
   }
 
   get branchName () {