Update box.html.md
Update box.html.md

Grammatical correction to Box Prune documentation 

Italicize Box Update "Note"
chrisroberts/vagrant,mitchellh/vagrant,PatrickLang/vagrant,bryson/vagrant,chrisroberts/vagrant,marxarelli/vagrant,taliesins/vagrant,taliesins/vagrant,gitebra/vagrant,mitchellh/vagrant,taliesins/vagrant,chrisroberts/vagrant,crashlytics/vagrant,mitchellh/vagrant,marxarelli/vagrant,mitchellh/vagrant,bryson/vagrant,sni/vagrant,chrisroberts/vagrant,sni/vagrant,gitebra/vagrant,PatrickLang/vagrant,sni/vagrant,crashlytics/vagrant,crashlytics/vagrant,bryson/vagrant,PatrickLang/vagrant,bryson/vagrant,crashlytics/vagrant,gitebra/vagrant,PatrickLang/vagrant,marxarelli/vagrant,taliesins/vagrant,sni/vagrant,gitebra/vagrant,marxarelli/vagrant