Using the latest shiny_1.1.0.9001 (and shinydashboard_0.7.0) the sidebar toggle icon (burger icon) isn't displayed correctly:
Firefox:

Chrome:

Might be related to this?
# if (!require("devtools"))
# install.packages("devtools")
# devtools::install_github("rstudio/shiny")
## app.R ##
library(shiny)
library(shinydashboard)
ui <- dashboardPage(
dashboardHeader(),
dashboardSidebar(),
dashboardBody()
)
server <- function(input, output) { }
shinyApp(ui, server)