Import print_function from __future__ for python compatibility

This alters the behaviour of python2's print statement to be compatible
with python3's print function. While not strictly necessary for now,
this might help future compatibility.
Thanks to Seppo Yli-Olli (@nanonyme) for suggesting this.

lsteamclient/gen_wrapper.py

@@ -3,6 +3,8 @@
 #NOTE: If you make modifications here, consider whether they should
 #be duplicated in ../vrclient/gen_wrapper.py
 
+from __future__ import print_function
+
 import pprint
 import sys
 import clang.cindex

proton

@@ -2,6 +2,8 @@
 
 #script to launch Wine with the correct environment
 
+from __future__ import print_function
+
 import filecmp
 import json
 import os

vrclient_x64/gen_wrapper.py

@@ -3,6 +3,8 @@
 #NOTE: If you make modifications here, consider whether they should
 #be duplicated in ../lsteamclient/gen_wrapper.py
 
+from __future__ import print_function
+
 import pprint
 import sys
 import clang.cindex