Description

Isolation Forest is executed in parallel during fitting. But, during prediction it is running single-threaded. This translates into being quite slow at prediction time.

Together with this issue I am submitting a PR that parallelises prediction.

Steps/Code to Reproduce

NA

Expected Results

NA

Actual Results

NA

Versions

python: 3.6.8
sklearn: 0.22.dev0
numpy: 1.16.4
scipy: 1.3.0
Cython: 0.29.9