Keyword changed: grunt-plugin to gruntplugin

The official keyword for grunt plugins is gruntplugin, this is how it can be searched for and how it'll show up on gruntjs.org (it doesn't now).
bump patch version
Added option to specify node `--harmony` flag

Also, you can now specify options.require as either an array or a string.
Merge branch 'sethmcl-master'
add harmony flag and release 1.5.0
move istanbul to peer dependency
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