add font-display tag to font-face for icons

_sass/dynare.scss

 /* Generated from https://icomoon.io/app */
 @font-face {
     font-family: 'icomoon';
+    font-display: block;
     src:  url('/assets/fonts/icomoon/icomoon.eot?z1c3c5');
     src:  url('/assets/fonts/icomoon/icomoon.eot?z1c3c5#iefix') format('embedded-opentype'),
           url('/assets/fonts/icomoon/icomoon.ttf?z1c3c5') format('truetype'),