#48 Make compatible with libplist 2.3.0.

[Theodore Ni]

Replace plist_dict_insert_item, which has been deprecated since version 1.11 released on March 21, 2014, with plist_dict_set_item.

It was deprecated in this commit: https://github.com/libimobiledevice/libplist/commit/6b719ecda2072dafeb98a44a6f4eac247748efc0

It was removed in this commit: https://github.com/libimobiledevice/libplist/commit/3fdb11126928717007127688f55a5fffa8a59ac9