"Build from Source" page states an outdated JDK version 7

[yurmix]

[Copied from website issue #470]

Problem:
The documentation page Build from Source states the following:

Building Druid requires the following: - JDK 7 or JDK 8

While in fact Druid mandates JDK 8 since version 0.10.0 (as evident in Druid pr #3914 by @gianm).

Solution:
Remove the text "JDK 7 or ".

[jihoonson]

@yurmix thanks. Do you want to make a PR for this issue?

[yurmix]

Oh, actually I have made one already: #6031
(I have mentioned the issue there, but not vice versa.)