title: Can't use comma as separator c3js
body: <p>I'm currently working on a evolution graph with the framework c3.js based on d3.js.</p>
  
  <p>I want to format the values of the Y axis that are numbers. I currently have this format : XX.X
  What I want is to use the comma as separator of decimals : XX,X</p>
  
  <p>I tried two methods :</p>
  
  <pre><code>y : {
              tick : {
                  values : steps, 
                  format : d3.format(",.1f")
              },
              min : steps[0],
              max : steps[steps.length-1]
           }
  </code></pre>
  
  <p>And to use the d3 formatter : </p>
  
  <pre><code> y : {
                  tick : {
                      values : steps, 
                      format : function(d) {
                          var s = d3.formatSpecifier("f");
                          s.precision = precisionFixed(0.1);
                          s.comma = true;
                          var f =  d3.format(s);
                          return f(d);
                       }
                  },
                  min : steps[0],
                  max : steps[steps.length-1]
               }
  </code></pre>
  
  <p>See doc here: <a href="https://github.com/d3/d3-format" rel="nofollow noreferrer">https://github.com/d3/d3-format</a></p>
  
  <p>But I get an error (d3.formatSpecifier is not a function...). Does someone already resolved this issue? </p>
  
  <p>Thank you</p>