title: shinydashboard tabItems not working
body: <p>I have a simple shiny dashboard that has four tabs in the side menu, and for some reason, when I build the shiny app, clicking on the side menu does not show me a new page, and the content of tab2 just appends itself to tab1. </p>
  
  <p>While searching stackoverflow showed me this question: <a href="https://stackoverflow.com/questions/30421596/shinydashboars-tabitems-not-working-properly?s=10|55.2601">Shinydashboars tabItems not working properly</a>, the answer doesn't apply to me since I'm not using rmd, and i don't plan to host it to a AWS server. </p>
  
  <p>Here is the code for reference:</p>
  
  <pre><code>ui &lt;- dashboardPage(
  dashboardHeader(title = "Study Dashboard"),
  dashboardSidebar(
  sidebarMenu(
    menuItem("Overall Objectives", tabName = "objectives"),
    menuItem("Wellpad Operator", tabName = "wellpad_operator"),
    menuItem("Wastewater Expert", tabName = "wastewater_expert"),
    menuItem("Freshwater Expert", tabName = "freshwater_expert"),
    menuItem("Environmental Impact", tabName = "environ_impact")
  )
  ),
  dashboardBody(
  #Tab 1 Objective View
  tabItems(
    tabItem(tabName = "objectives", 
            h2("Overall Objectives"),
            fluidRow(
              box(
                title = "Overall Objective Comparison", width = 6, solidHeader = TRUE,
                plotOutput("objective_plot")
              ),
              box(
                title = "Cost Category Breakdown", width = 6, solidHeader = TRUE,
                plotOutput("costbreakdown_plot")
              ),
              box(
                title = "Decision Variables", width = 12, solidHeader = TRUE,
                tableOutput("decision_table"))
            ))
  ),
  
  #Tab 2 Wellpad Decision
  tabItem(tabName = "wellpad_operator", 
          h2("Wellpad Operator") 
          ),
  
  #Tab 3 Wastewater Expert
  tabItem(tabName = "wastewater_expert",
          h2("Wastewater Expert")
          ),
  
  #Tab 4 Freshwater Expert
  tabItem(tabName = "freshwater_expert",
          h2("Freshwater Expert")
          ),
  
  #Tab 5 Environmental Damages
  tabItem(tabName = "environ_impact",
          h2("Environmental Impact"))
  )
  )
  
  server &lt;- function(input, output) {
  #server side code that generates the plots
  }
  
  shinyApp(ui = ui, server = server)
  </code></pre>
  
  <p>Thanks for all your help!</p>