Update util.py

Changed line 41 so that the logarithmic change to base 1000 formula uses log base 10  instead of natural log. this allows the denominator to be simplified to 3. Also got rid of the use of floor() inside of int() because it is redundant.

pygal/util.py

@@ -38,7 +38,7 @@ def float_format(number):
 
 def humanize(number):
     """Format a number to engineer scale"""
-    order = number and int(floor(log(abs(number)) / log(1000)))
+    order = number and int(log10(abs(number)) / 3.0)
     human_readable = ORDERS.split(" ")[int(order > 0)]
     if order == 0 or order > len(human_readable):
         return float_format(number / (1000 ** int(order)))