suppress the import json warning when generating _version

Author: jreback

versioneer.py

@@ -1130,7 +1130,9 @@ def versions_from_parentdir(parentdir_prefix, root, verbose):
 # unpacked source archive. Distribution tarballs contain a pre-generated copy
 # of this file.
 
-import json
+from warnings import catch_warnings
+with catch_warnings(record=True):
+    import json
 import sys
 
 version_json = '''