Fix bulma-slider SASS inclusion

Bulma slider 2.0.4 sass files are no longer in dist/css directory.

src/styles.scss

@@ -2,7 +2,7 @@
 
 @import '../node_modules/mapbox-gl/dist/mapbox-gl.css';
 @import '~scss/init_bulma.scss';
-@import '../node_modules/bulma-slider/dist/css/bulma-slider.sass';
+@import '../node_modules/bulma-slider/src/Sass/index.sass';
 @import '../node_modules/bulma-checkradio/dist/css/bulma-checkradio.sass';
 @import '../node_modules/bulma-tooltip/dist/css/bulma-tooltip.min.css';
 @import './scss/custom-hamburger.scss';