Fix precision in activity chart.

diff --git a/pygit/chart.py b/pygit/chart.py
index 022900a..167a74a 100644
--- a/pygit/chart.py
+++ b/pygit/chart.py
@@ -62,7 +62,7 @@ class Chart(object):
     self.hash += hash(tuple(lst))

   def labels(self,lst):
-    step_x = (self.width-pl-pr)/(len(lst)-1)
+    step_x = float(self.width-pl-pr)/(len(lst)-1)
     self.cx.set_source_rgb(0,0,0)
     for pc in self.places:
       pc.move_to(0,0)
@@ -76,7 +76,7 @@ class Chart(object):
       self.cx.stroke()
       cur_x += step_x
     cur_x = pl
-    self.cx.set_source_rgb(0,0,0)
+    self.cx.set_source_rgb(0.2,0.2,0.2)
     for i in range(len(lst)):
       label = lst[i]
       self.cx.move_to(cur_x, int(self.height-py/2))