Only replace the first instance of 'preview'.
Only replace the first instance of 'preview'.

Previously, if the user wanted to preview a meme but they used the word
preview in the text, all instances of ‘preview’ were being removed. We
only want to replace the first instance.

nicolewhite/slack-meme,tezzutezzu/slack-meme,joeynebula/slack-meme,DuaneGarber/slack-meme