Update of Apache Spark and Python 3.6 compatibility

Now the Apache-Spark has released two stable version, 2.1.1 and 2.2.0. The compatibility problem has been solved, you don’t need to try pyenv anymore. Just install apache-spark from home-brew then you may use it.

But if you are going to use python3.6 and your default python in terminal is python2.7, you would find that the REPL would still be the python2.7 version.