Update easyimage.js

Hi,
I modified the thumbnail generation commands slightly, thought I'd give you a pull request, feel free to use or ignore as you see appropriate :)

However, I'd definitely recommend using "-strip" for thumbnails to remove all the metadata.

Changes:
Using "-thumbnail" to create thumbnail (appears to be twice as fast).
Using "-interpolate bicubic" to better mimic Photoshop's "save for web"
Using "-strip" to remove color profile, etc as it's not needed for thumbnails (greater than 50% file size saving on a thumbnail of 300x300px, much bigger file size saving on smaller ones).