You can use the command below to Install BitNinja and then the WHM plugin:
wget -qO- https://get.bitninja.io/bitninja-whm.tar.gz | tar -zx && ./bitninja-whm/install --license_key=[licensekey]

Or you can use the command below to install the WHM plugin only:
wget -qO- https://get.bitninja.io/bitninja-whm.tar.gz | tar -zx && ./bitninja-whm/install --no_install_bitninja