title: Unwanted lines appearing in html5 canvas using tiles
body: <p>I'm drawing a map on a canvas using squares 40px * 40px. 
  All is well until I, by offsetting the canvas (using transform), scroll the map. Then, out of nowhere, lines apear between the tiles. See images below.</p>
  
  <p>Why?</p>
  
  <p><img src="https://i.stack.imgur.com/IRVYm.png" alt="Canvas drawn, but no offset yet. All is fine"> <img src="https://i.stack.imgur.com/oboD7.png" alt="Canvas drawn w offset, now where did those lines come from?"></p>