Python 3.6 invalid escape sequence deprecation fixes (#177)

https://docs.python.org/3/whatsnew/3.6.html#deprecated-python-behavior
diff --git a/examples/c_json.py b/examples/c_json.py
index 3bfef5b..2b33360 100644
--- a/examples/c_json.py
+++ b/examples/c_json.py
@@ -49,7 +49,7 @@
 from pycparser.plyparser import Coord
 
 
-RE_CHILD_ARRAY = re.compile('(.*)\[(.*)\]')
+RE_CHILD_ARRAY = re.compile(r'(.*)\[(.*)\]')
 RE_INTERNAL_ATTR = re.compile('__.*__')