title: Factor dropdown filter in DT::datatable in shiny dashboards not working
body: <p>Is it just me or is it a bug that if i have a factor column and I add filter with DT, the dropdown get cut-off in shiny dashboard.</p>
  
  <p>I am using mtcars as an example and I make cyl as a factor. (the numeric slider filter works fine, but the factor filter dont). Here is the code and the screen shot. </p>
  
  <pre><code>## app.R ##
  library(shinydashboard)
  library(dplyr)
  
  
  mtcars$cyl &lt;- as.factor(mtcars$cyl)
  
  ui &lt;- dashboardPage(
    dashboardHeader(title = "Simple Dashboard"),
    ## Sidebar content
    dashboardSidebar(sidebarMenu(
      menuItem(
        "Dashboard", tabName = "dashboard", icon = icon("dashboard")
      ),
      menuItem("Widgets", tabName = "widgets", icon = icon("th"))
    )),
    ## Body content
    dashboardBody(tabItems(
      # First tab content
      tabItem(tabName = "dashboard",
              fluidRow(
                box(plotOutput("plot1", height = 250)),
  
                box(
                  title = "Controls",
                  sliderInput("slider", "Number of observations:", 1, 100, 50)
                )
              )),
  
      # Second tab content
      tabItem(tabName = "widgets",
              fluidRow(DT::dataTableOutput('items_dt')))
    ))
  )
  
  server &lt;- function(input, output) {
    set.seed(122)
    histdata &lt;- rnorm(500)
  
    output$plot1 &lt;- renderPlot({
      data &lt;- histdata\[seq_len(input$slider)\]
      hist(data)
    })
  
    output$items_dt = DT::renderDataTable(
      mtcars,
      filter = 'bottom',
      options = list(scrollX = TRUE)
    )
  }
  
  shinyApp(ui, server)
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/lvDPL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lvDPL.png" alt="Factor filters get cut-off"></a></p>
  
  <p><a href="https://i.stack.imgur.com/plhPQ.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/plhPQ.png" alt="Numeric sliders work fine"></a></p>