Plug a memory leak.

Addressing:
 37 bytes in 1 blocks are definitely lost in loss record 2 of 3
    at 0x4A0645D: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
    by 0x31EAC860B9: strdup (in /usr/lib64/libc-2.18.so)
    by 0x4C5DBDA: oscap_strdup (util.c:65)
    by 0x4CB1AEF: xccdf_session_set_report_export (xccdf_session.c:291)
    by 0x40B9D1: app_evaluate_xccdf (oscap-xccdf.c:507)
    by 0x4079BF: oscap_module_process (oscap-tool.c:261)
    by 0x4069BE: main (oscap.c:79)
Plug a memory leak.
Addressing:
 4 bytes in 1 blocks are definitely lost in loss record 1 of 1
    at 0x4A0645D: malloc (in /usr/lib64/valgrind/vgpreload_memcheck-amd64-linux.so)
    by 0x31EAC860B9: strdup (in /usr/lib64/libc-2.18.so)
    by 0x4C5DBDA: oscap_strdup (util.c:65)
    by 0x4C9743C: cpe_parser_ctx_set_schema_version (cpe_ctx_priv.c:97)
    by 0x4C99A37: cpe_generator_parse (cpedict_priv.c:710)
    by 0x4C9B2C9: cpe_dict_model_parse (cpedict_priv.c:644)
    by 0x4C9B4C9: cpe_dict_model_parse_xml (cpedict_priv.c:580)
    by 0x4C955E2: cpe_dict_model_import (cpedict.c:56)
    by 0x40CBE1: app_info (oscap-info.c:220)
    by 0x4079BF: oscap_module_process (oscap-tool.c:261)
    by 0x4069BE: main (oscap.c:79)
Merge pull request #8 from jan-cerny/maint-1.0

Plug a memory leak.