change clearfix mixin to drop parens that prevent it from being a class, too

docs/assets/css/bootstrap-responsive.css

@@ -7,6 +7,16 @@
  *
  * Designed and built with all the love in the world @twitter by @mdo and @fat.
  */
+.clearfix {
+  *zoom: 1;
+}
+.clearfix:before, .clearfix:after {
+  display: table;
+  content: "";
+}
+.clearfix:after {
+  clear: both;
+}
 .hidden {
   display: none;
   visibility: hidden;

docs/assets/css/bootstrap.css

@@ -94,6 +94,16 @@ textarea {
   overflow: auto;
   vertical-align: top;
 }
+.clearfix {
+  *zoom: 1;
+}
+.clearfix:before, .clearfix:after {
+  display: table;
+  content: "";
+}
+.clearfix:after {
+  clear: both;
+}
 body {
   margin: 0;
   font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;