[DOCS] Modernize reference to the Incubator
[DOCS] Modernize reference to the Incubator

Instead of "accepted into", say when Impala
"graduated from".

Change-Id: I9681414b0e2031c62d522c98a9bcb5f74b4a3480
Reviewed-on: http://gerrit.cloudera.org:8080/8647
Reviewed-by: Jim Apple <396f577ccd0f19e47f0fb44dae1d6fc43cc20400@apache.org>
Tested-by: Impala Public Jenkins

cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala,cloudera/Impala