Use <pre> tag for lines instead of using white-space: pre css property

One less CSS rule, since the whitespace behavior of a `pre` tag is already baked into the browser's default styles.

src/app/editor.coffee

@@ -669,7 +669,7 @@ class Editor extends View
     selectionView.remove() for selectionView in @getSelectionViews()
 
   calculateDimensions: ->
-    fragment = $('<div class="line" style="position: absolute; visibility: hidden;"><span>x</span></div>')
+    fragment = $('<pre class="line" style="position: absolute; visibility: hidden;"><span>x</span></div>')
     @renderedLines.append(fragment)
 
     lineRect = fragment[0].getBoundingClientRect()
@@ -812,7 +812,7 @@ class Editor extends View
             lineAttributes.class += ' selected'
         else
           lineAttributes = { class: 'line' }
-        @div lineAttributes, =>
+        @pre lineAttributes, =>
           if line.text == ''
             @raw '&nbsp;' if line.text == ''
           else

static/editor.css

@@ -72,12 +72,6 @@
   width: 100%;
 }
 
-.editor .line, .gutter .line-number {
-  white-space: pre;
-  margin: 0;
-  padding: 0;
-}
-
 .editor .line > span {
   vertical-align: top;
 }