Fix for issue#30 livereload permissions error on windows machines

My first ever pull request, hope I've done it right :-)

Gruntfile was creating an issue with livereload resulting in a permissions error on windows machines - see issue #30 - seems to be an infinite loop. Livereload watched for html files in the .jekyll folder. This was changed to watch changes to posts - .md files - and the layout and index html files. This fixed the issue for me and allowed livereload updates to continue.