Fix SlowBuffer.write() with 'ucs2' throws ReferenceError.

lib/buffer.js

@@ -100,7 +100,7 @@ SlowBuffer.prototype.write = function(string, offset, encoding) {
 
     case 'ucs2':
     case 'ucs-2':
-      return this.ucs2Write(start, end);
+      return this.ucs2Write(string, offset);
 
     default:
       throw new Error('Unknown encoding');

test/simple/test-buffer.js

@@ -500,3 +500,8 @@ console.log(z.length)
 assert.equal(2, z.length);
 assert.equal(0x66, z[0]);
 assert.equal(0x6f, z[1]);
+
+
+var b = new SlowBuffer(10);
+b.write('あいうえお', 'ucs2');
+assert.equal(b.toString('ucs2'), 'あいうえお');