Fix raise statement (py3)

Author: vbraun

src/sage/functions/piecewise.py

@@ -794,7 +794,7 @@ def integral(cls, self, parameters, variable, x=None, a=None, b=None, definite=F
                 return F(b) - F(a)
 
             if a != None or b != None:
-                raise TypeError, 'only one endpoint given'
+                raise TypeError('only one endpoint given')
 
             area = 0
             new_pieces = []