Update app.css

Solve the problem that: When open the index.html by IE11, contents of the footer aren't top-align.

Author: Fental

public/css/app.css

@@ -23,6 +23,7 @@ input[type='radio']           { border: 0; }
 }
 #footer                       { padding-top: 10px; font-size: 13px; color: rgba(255, 255, 255, 0.7); text-shadow: 0 1px 1px rgba(0, 0, 0, 0.2); border-top: 1px solid #797f85; border-top-color: rgba(0, 0, 0, 0.15); box-shadow: inset 0 1px 1px 0 rgba(255, 255, 255, 0.2); vertical-align: top; text-align: center; }
 #footer a                     { vertical-align: top; color: #fff; }
+#footer span                     { vertical-align: top;}
 .clr:after                    { clear:both; content:"."; display: block; height:0; visibility: hidden; line-height:0; font-size:0; }
 
 .ir                           { border: 0; font: 0/0 a; text-shadow: none; color: transparent; background-color: transparent; }