title: pandas reading a csv with decimal separator comma is not changing all values
body: <p>I have a csv file with a column KG and it is specified with a decimal separator as ","(comma).</p>
  
  <pre><code>KG
  267,890
  458,987
  125,888
  1,55
  2,66
  </code></pre>
  
  <p>When I use <code>pd.read_csv(file_name,sep=';', decimal=",")</code>, only the values 1,55 and 2,66 are converted to 1.55 and 2.66 respectively.
  the vales with 3 digits before the comma stay the same.</p>
  
  <p>This is the <strong>output</strong></p>
  
  <pre><code>KG
  267,890
  458,987
  125,888
  1.55
  2.66
  </code></pre>
  
  <p>Please can someone guide me through how to change all values to have a dot, as well to <strong>use dtype as float64 for the column</strong></p>