Update through2

I was having the following bug with gulp-less on node v0.12.7:

```[03:11:57] TypeError: Cannot read property 'on' of undefined
    at DestroyableTransform.Readable.pipe (/Users/liam/Sites/wiringtheworld.com/jekyll/node_modules/gulp-less/node_modules/through2/node_modules/readable-stream/lib/_stream_readable.js:516:7)
    at Gulp.<anonymous> (/Users/liam/Sites/wiringtheworld.com/jekyll/gulpfile.js:26:36)
    at module.exports (/Users/liam/Sites/wiringtheworld.com/jekyll/node_modules/gulp/node_modules/orchestrator/lib/runTask.js:34:7)
    at Gulp.Orchestrator._runTask (/Users/liam/Sites/wiringtheworld.com/jekyll/node_modules/gulp/node_modules/orchestrator/index.js:273:3)
    at Gulp.Orchestrator._runStep (/Users/liam/Sites/wiringtheworld.com/jekyll/node_modules/gulp/node_modules/orchestrator/index.js:214:10)
    at Gulp.Orchestrator.start (/Users/liam/Sites/wiringtheworld.com/jekyll/node_modules/gulp/node_modules/orchestrator/index.js:134:8)
    at /usr/local/lib/node_modules/gulp/bin/gulp.js:129:20
    at process._tickCallback (node.js:355:11)
    at Function.Module.runMain (module.js:503:11)
    at startup (node.js:129:16)```

And updating to through2 v0.6.5 fixed the issue for me.

package.json

@@ -23,7 +23,7 @@
     "gulp-util": "^3.0.4",
     "less": "^2.4.0",
     "object-assign": "^2.0.0",
-    "through2": "^0.6.3",
+    "through2": "^0.6.5",
     "vinyl-sourcemaps-apply": "^0.1.4"
   },
   "devDependencies": {