fixed small issue in example code

Author: savon-noir

examples/json_serialize.py

@@ -1,6 +1,5 @@
 from libnmap.parser import NmapParser
 from libnmap.reportjson import ReportDecoder, ReportEncoder
-import os
 import json
 
 nmap_report_obj = NmapParser.parse_fromfile('libnmap/test/files/1_hosts.xml')