title: Add ylab to ggplot with fivethirtyeight ggtheme
body: <p>Is it possible to add a label to the y axis if you are using <code>theme_fivethirtyeight</code>? I tried <code>ylab</code> but it does not work:</p>
  
  <pre><code>library(ggplot2)
  library(ggthemes)
  p2 &lt;- ggplot(mtcars, aes(x = wt, y = mpg, colour = factor(gear))) +
    geom_point() +
    ggtitle("Cars")
  p2 + geom_smooth(method = "lm", se = FALSE) +
    scale_color_fivethirtyeight("cyl") +
    theme_fivethirtyeight() + ylab('SOMETHING')
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/cpJDd.png" rel="noreferrer"><img src="https://i.stack.imgur.com/cpJDd.png" alt="enter image description here"></a></p>