create many processes when importing librosa

[Tianhua Zhao]

ENV:
ubuntu 16.04
python 3.5
librosa 0.6.3
pyinstaller 3.4

reproduction steps:

create a test.py file which context is

import librosa
print("hello world")

result of "python3 test.py" is expected.

But "pyinstaller test.py", "./dist/test/test" will create many processes and print many 'hello world'.