fix CallbackLogger's format

tp2_invgeom/main.asciidoc

@@ -42,7 +42,7 @@ class CallbackLogger:
      def __init__(self):
           self.nfeval = 1
      def __call__(self,x):
-          print '===CBK=== {0:4d}   {1: 3.6f}   {2: 3.6f}'.format(self.nfeval, x[0], x[1], cost(x))
+          print '===CBK=== {0:4d}   {1: 3.6f}   {2: 3.6f}   {3: 3.6f}'.format(self.nfeval, x[0], x[1], cost(x))
           self.nfeval += 1
 
 x0 = np.array([0.0,0.0])