HTMLReporter symbols are inline-block rather than floated

On a very large test suite (8000 specs), a significant amount
of time is spent just drawing the spec dots. Some sort of
worse-than-linear artifact that summons itself only when you
have 8000 floated elements trying to hang out together.

This performance penalty is not seen with inline-block.

In Chrome 29:
  Floated dots: 16.795s
  Inline-block dots: 2.774s

Setting the dots to 'display: none;' takes about the same time
as the inline-block figure, so this is probably a low enough bound
(no need for chunked rendering or who knows what).

src/html/_HTMLReporter.scss

@@ -93,11 +93,9 @@ body {
     margin: $line-height 0;
 
     li {
-      display: block;
-      float: left;
+      display: inline-block;
       height: $line-height / 2;
       width: $line-height;
-      margin-bottom: $line-height / 2;
 
       font-size: 16px;