fix compile of toft/storage/path

N/A

To use getcwd as defined in POSIX, unistd.h should be included.

http://pubs.opengroup.org/onlinepubs/9699919799/functions/getcwd.html

Change-Id: I621176f4db9cf1fd6719bd91c855493c7342678d
Signed-off-by: liuhuahang <liuhuahang@xiaomi.com>
Merge pull request #114 from huahang/master

fix compile of toft/storage/path