Change "print the sum" to "returns ..." in "f2"

The print statements starting on line 17 will print out "None" if the function "f2" is written as described in the instructions. 
This change will make the comments next to the print statements accurate.

Author: HakujouRyu

src/11_args.py

@@ -8,7 +8,7 @@
 
 print(f1(1, 2))
 
-# Write a function f2 that takes any number of integer arguments and prints the
+# Write a function f2 that takes any number of integer arguments and returns the
 # sum.
 # Note: Google for "python arbitrary arguments" and look for "*args"