Center .icon-prev and .icon-next

Center .icon-prev and .icon-next the same way .glyphicon icon are.
And this is the html markup:
<a class="left carousel-control" href="#carousel-main-menu" role="button" data-slide="prev">
<span class="icon-prev" aria-hidden="true"></span>
</a>

less/carousel.less

@@ -148,6 +148,7 @@
     width:  20px;
     height: 20px;
     margin-top: -10px;
+    line-height: 1;
     font-family: serif;
   }