add jshint as an explicit dependency
add jshint as an explicit dependency

otherwise, if it's not installed, npm shrinkwrap says
npm ERR! peer invalid: jshint@2.x, required by gulp-jshint@2.0.0

if it's installed, npm shrinkwrap says
npm ERR! extraneous: jshint@2.9.1 /path/to/rainloop-webmail/node_modules/jshint

RainLoop/rainloop-webmail,RainLoop/rainloop-webmail,Oygron/rainloop-webmail,Oygron/rainloop-webmail,phunehehe/rainloop-webmail,robertol/rainloop-webmail,robertol/rainloop-webmail,RainLoop/rainloop-webmail,phunehehe/rainloop-webmail,phunehehe/rainloop-webmail,RainLoop/rainloop-webmail,robertol/rainloop-webmail,Oygron/rainloop-webmail,robertol/rainloop-webmail