need to add json files in (#184)

Author: kratsg

setup.py

@@ -7,7 +7,7 @@
 from setuptools import setup
 
 datafile = "src/skhep_testdata/data"
-data_ex = {".root", ".lhe", ".gz"}
+data_ex = {".root", ".lhe", ".gz", ".json"}
 
 data_files = {n for n in os.listdir(datafile) if any(n.endswith(ex) for ex in data_ex)}