title: rCharts Highcharts change xAxis labels
body: <p>So I am trying to make a plot with the x-axis reading as the dates in my data.frames.
  However it keeps reading as 0,1,2,3,4,5,....,,20, instead of April-01,April-02...April-29</p>
  
  <pre><code> data.setup&lt;-function(data,loc='yahoo',start.date=Sys.Date()-months(1),
                                        end.date=Sys.Date()) {
    getSymbols(data,src=loc)
    x&lt;-as.data.frame(window(get(data),
              start=as.character(start.date),
              end=as.character(end.date)))
    x$dates&lt;-row.names(x)
    colnames(x)&lt;-c('Open','High','Low','Close','Volume','Adjusted','Dates')
    x&lt;-x[c(7,1,2,3,4,5,6)]
    return(return(x))
  }
  
  data&lt;-data.setup('AAPL',start.date=Sys.Date()-months(1))  
  h1&lt;-Highcharts$new()
  h1$chart(type='line')
  h1$xAxis(category=data$Dates,id='dates')
  h1$series(data=data$Low,name='Low',xAxis='dates')
  </code></pre>