title: module 'statsmodels.tsa.api' has no attribute 'arima_model'
body: <p>I'm trying to use "statsmodels.api" to work with time series data and trying to fit a simple ARIMA model using</p>
  
  <pre><code>sm.tsa.arima_model.ARIMA(dta,(4,1,1)).fit()
  </code></pre>
  
  <p>but I got the following error</p>
  
  <pre><code>module 'statsmodels.tsa.api' has no attribute 'arima_model'
  </code></pre>
  
  <p>I'm using '<code>statsmodels</code>' version 0.9.0 with '<code>spyder</code>' version 3.2.8 I'd be pleased to get your help thanks</p>