Fix error adding class to copy buttons

The quotes arround the class assignment had not been properly escaped.
This was causing PHP to fail and return a blank page.

clock.css

@@ -7,3 +7,6 @@ select {
 .chkbox {
   display: inline-block;
 }
+.time_copy_btn {
+  margin-left: 5px;
+}

clock.php

@@ -48,13 +48,13 @@
           "<br><span>".
           "<p id='time_body'>".
           date("D, M d, Y, H:i:s") .
-          "</p><p> GMT". date("O T") ."</p><button onclick='copy_timestamp(\"time_body\")'>Copy Timestamp</button>\n\t\t</span>";
+          "</p><p> GMT". date("O T") ."</p><button class=\"time_copy_btn\" onclick='copy_timestamp(\"time_body\")'>Copy Timestamp</button>\n\t\t</span>";
         if($_POST['originalTZ']){// if the user want display the browser detected timezone as well as the selected one.
           date_default_timezone_set($originalTZ);
           echo'<h3>Time in original Timezone</h3>'.
           '<span><p id="time_original">'.
           date("D, M d, Y, H:i:s") .
-          "</p><p> GMT". date("O T") ."</p><button onclick='copy_timestamp(\"time_original\")'>Copy Timestamp</button></span>";
+          "</p><p> GMT". date("O T") ."</p><button class=\"time_copy_btn\" onclick='copy_timestamp(\"time_original\")'>Copy Timestamp</button></span>";
           date_default_timezone_set($scriptTZ);
         }
         if($_POST['displayOffset']){