'hash:images' in Gruntfile.coffee only 'hash' them, need to 'bust' them too

[mlhch]

For example, if we place a image file to src/images/foo.png or src/styles/images/bar.png, and then we want to reference it in src/index.html or src/styles/styles.less, then bug will appears if we run 'grunt prod'.

Obviously, the foo.png and bar.png was renamed as foo.xxxxxxx.png and bar.xxxxxxx.png, but in src/index.html and background-image:url(styles/images/bar.png) in src/styles/styles.less not updated.

However, the 'bust' task in grunt-hustler need to be upgraded for this purpose