Fix the bug in issue#120 "NameError: name 'metadata' is not defined"

[shuiyujinlan]

Simply remove the multiprocessing module and use "for loop" to receive data in suspicious trees. This is usable but may slow down the process in handling big data. It will be better if someone fix the bug inside the multiprocessing module, which caused the NameError in suspicious_clades. I fix it this way just because I'm not familiar to multiprocessing.