Update copyright year to 2018

Author: mu-hun

index.html

@@ -118,7 +118,7 @@ <h5 class="white-text">Links</h5>
             </div>
             <div class="footer-copyright">
                 <div class="container">
-                    &copy; 2014-2017 if-Team
+                    &copy; 2014-2018 if-Team
                     <div class="right">
                     <a class="white-text">View on</a>
                     <a class="octicon octicon-logo-github white-text" href="https://github.com/if-Team/if-Team.github.io"></a>