Update PLDI15-AEC.README.md

Author: daejunpark

PLDI15-AEC.README.md

@@ -8,7 +8,7 @@
  * VM image: 
    * VMWare: [[ova]](http://fslweb.cs.illinois.edu/kjs/kjs.vmware.ova) (~3.5GB) |
              [[md5]](http://fslweb.cs.illinois.edu/kjs/kjs.vmware.ova.md5)
-   * VirtualBox: [[ova]](http://fslweb.cs.illinois.edu/kjs/kjs.virtualbox.ova) (~2.7GB) |
+   * VirtualBox: [[ova]](http://fslweb.cs.illinois.edu/kjs/kjs.virtualbox.ova) (~2.8GB) |
                  [[md5]](http://fslweb.cs.illinois.edu/kjs/kjs.virtualbox.ova.md5)
    * login: kjs, passwd: kjs
    * artifact location: `/home/kjs/javascript-semantics`