title: How to change the histogram borderline thickness in ggplot geom_histogram()
body: <p>I have the following code:</p>
  
  <pre><code>library(ggplot2)
  data(mtcars)
  ggplot(mtcars, aes(x=mpg)) + geom_histogram(bins=15, colour='red')
  </code></pre>
  
  <p>Which produce this:</p>
  
  <p><a href="https://i.stack.imgur.com/5PZAZ.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/5PZAZ.jpg" alt="enter image description here"></a></p>
  
  <p>As stated there, how can I change the  thickness of the enclosing line of the histogram?</p>