macos: make installer link to correct aardvark library 

Building pmbusorgcli with pyinstaller currently results in the linux library getting linked instead of macos, leading to this error:

`ValueError: Unknown Mach-O header: 0x7f454c46 in <_io.BufferedReader name='/Users/vgani/.pyenv/versions/3.6.3/lib/python3.6/site-packages/aardvark_py/aardvark/linux/arch64/aardvark.so'>`