Set width: auto on div.prompt
Set width: auto on div.prompt

Fixes ehmatthes#38
Props @Tanner
BadWizard/intro_programming,chenleo/ipynotebook,chenleo/ipynotebook,BadWizard/intro_programming,BadWizard/intro_programming,nntisapeh/intro_programming,BadWizard/intro_programming,chenleo/ipynotebook,chenleo/ipynotebook,nntisapeh/intro_programming,nntisapeh/intro_programming,ehmatthes/intro_programming,ehmatthes/intro_programming,ehmatthes/intro_programming,ehmatthes/intro_programming,nntisapeh/intro_programming