title: Shiny apps icon with "-" in the name
body: <p>I'm creating a shiny app and have come across an issue that i can't seem to find a solution to. I'm using shiny dashboard and am creating a menu system in the sideboard, and i would like to add some icons to the tabs. This works fine for all icons that does not have a - in the name, but i can't seem to figure out the once that do.</p>
  
  <pre><code>dashboardSidebar(
  sidebarMenu(
    menuItem("General statistics", tabName= "general_stat", icon = icon("check")),
    menuItem("Multiple regressions", tabName= "mult_reg", icon = icon("code-branch"))
  )
  </code></pre>
  
  <p>The "check" icon appears but not the "code-branch". What am i doing wrong?</p>
  
  <p>This may be a simple issue, but I just can't seem to figure it out.</p>