Update index.html

public/index.html

@@ -195,6 +195,7 @@
         <button class="btn" style="background-color: lightgray;" id="filter2021" onclick="filter(2021)">2021</button>
         <button class="btn" style="background-color: lightgray;" id="filter2020" onclick="filter(2020)">2020</button>
         <button class="btn" style="background-color: lightgray;" id="filter2019" onclick="filter(2019)">2019</button>
+        <button class="btn" style="background-color: lightgray;" id="filter2018" onclick="filter(2018)">2018</button>
         <!--<button class="btn" style="background-color: lightgray;" id="filter2020" onclick="filter(2018)">2018</button>-->
     </div>
     <div class="container" id="cont_paper">