Fix for ReadTheDocs when scikit-learn is not installed.
Fix for ReadTheDocs when scikit-learn is not installed.

gticket/scikit-neuralnetwork,capitancambio/scikit-neuralnetwork,IndraVikas/scikit-neuralnetwork,agomariz/scikit-neuralnetwork,KhanSuleyman/scikit-neuralnetwork,aigamedev/scikit-neuralnetwork,freakynit/scikit-neuralnetwork