title: Matplotlib: numbers in xaxis are shown disordered
body: <p>I'm trying to plot a simple diagram from a file, having time in xaxis and ms of responses in yaxis. So, I have this code:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  
  lines = [line.strip() for line in open('pingLog.txt')]
  
  time = []
  ms = []
  for i, x in enumerate(lines):
      t, m = x.split(',')
      time.append(t)
      ms.append(m)
  
  plt.plot(time, ms)
  plt.grid(True)
  plt.show()
  </code></pre>
  
  <p>The 'pingLog.txt' file has this values:</p>
  
  <pre><code>0,4
  2,5
  4,6
  6,7
  8,8
  10,9
  12,10
  </code></pre>
  
  <p>But when I run it, I get this result:</p>
  
  <p><a href="https://i.stack.imgur.com/6AzlO.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6AzlO.jpg" alt="enter image description here"></a></p>