…nk. Also bump Flume version to 1.6.0

Author: Hari Shreedharan <hshreedharan@apache.org>

Closes #6910 from harishreedharan/remove-commons-lang3 and squashes the following commits:

9875f7d [Hari Shreedharan] Revert back to Flume 1.4.0
ca35eb0 [Hari Shreedharan] [SPARK-8483][Streaming] Remove commons-lang3 dependency from Flume Sink. Also bump Flume version to 1.6.0