How can I use formattable with reactive tables ?

Here's a reproducible example :

```
library(DT)
library(shiny)
library(shinydashboard)
library(formattable)
ui <- dashboardPage(
dashboardHeader(),
dashboardSidebar(
selectizeInput("v.dependent", "", choices = names(mtcars),
selected = "mpg", multiple = FALSE),
selectizeInput("predictor", "", choices = names(mtcars),
selected = "disp",
multiple = TRUE)),
dashboardBody(
tabsetPanel(
tabPanel("test with mtcars",
box(formattableOutput("tab"))
)
)
)
)
server <- function(input, output) {
dep.var <- reactive({
out <- input$v.dependent
out
})
ind.var <- reactive({
out <- input$predictor
out
})
var.selected <- reactive({
out <- append(ind.var(), dep.var(), 0)
out
})
user.selection <- reactive({
mtcars[, names(mtcars) %in% var.selected()]
})
lmod <- reactive({
lm(as.formula(paste(input$v.dependent, "~", paste(input$predictor, collapse = "+"))), data = user.selection())
})
output$tab <- renderFormattable({
tmp <- summary(lmod())$coefficients
colnames(tmp) <- c("Coefficients", "SD", "t statistic", "Pvalue")
tmp <- signif(x = tmp, digits = 3)
tmp <- formattable(tmp, list(Pvalue = formatter("span",
style = x ~ style(color = ifelse(x < 0.05, style(color = "red", "black")))
)))
})
}
shinyApp(ui, server)
```

I know how to do with "static" tables but when I try with this code, I've got the error :

```
Warning: Error in formatC: 'format' must be one of {"f","e","E","g","G", "fg", "s"}
```

Any idea how to solve it ?