Spark and Elasticsearch supported version Update in Architecture Document

In the Architecture document on the official website.
http://predictionio.apache.org/system/

These lines:

• Apache Spark up to 1.6.3 for Hadoop 2.6 (not Spark 2.x version)
• Elasticsearch up to 1.7.5 (not the Elasticsearch 2.x version)

Seem to be out of date for quite a while.

After checking the current issues, it seems that PIO already supports Spark 2.X and Elasticsearch 5.X.

The current wording is a bit misleading and will make people think that the project hasn't been updated for a while.
I think we can update the wording and state that these are the minimum required version, like what had been done in the install section.
http://predictionio.apache.org/install/