How to add labels to x-axis when using nplot from the rChart package

Question

I have tried

require(rCharts); library(datasets); library(knitr); library(tidyverse)

loan_data_set <- read_csv("loan_data_set.csv")

loandata = as.data.frame(loan_data_set)

loandata$Gender <- as.factor(loandata$Gender)

loandata$Married <- as.factor(loandata$Married)

loandata$Education <- as.factor(loandata$Education)

# created a nPlot object

n1 <- nPlot(ApplicantIncome ~ Education, group = 'Married', type = 'multiBarChart', data = loandata)

This gives me the following graph

However, I do not know why the labels to the x-axis do not appear