Update app.js to handle SOSL 2 character minimum search term length

doSearch uses SOSL to perform a full text search on Contact. I added a simple check for the length of the searchTerm input into the search so that if it is fewer than 2 characters no search is performed. 

I was doing this in conjunction with an onchange event search feature I was playing around with which I might check-in later. If it is on a button click, you might want to give feedback to the user that no search in fact took place. Or perhaps revert to SOQL on the name field in case of single character. I've not played with that logic yet.