Fix font-family syntax in index.styl (#332)

Author: beccamarkowitz

src/.vuepress/styles/index.styl

@@ -47,7 +47,7 @@ a.sidebar-link.active
   margin-right 5px
 
 #app .site-name 
-  font-family: Roobert;
+  font-family "Roobert"
 
 // Navigation