Set LineWrapper.maxLength based on lines width, not editor with.

Because there's a gutter now that doesn't count.

src/atom/editor.coffee

@@ -219,7 +219,7 @@ class Editor extends View
   setMaxLineLength: ->
     maxLength =
       if @softWrap
-        Math.floor(@width() / @charWidth)
+        Math.floor(@lines.width() / @charWidth)
       else
         Infinity