postgres version doc update

[bleonard]

What

I was running airbyte on an old computer that had Postgres 9.4 on it. The docs said it would be ok.
But I received these kind of errors when syncing (source: github, destination: postgres).

create  index if not exists
"ba498949f97eb58edc0d479256d87145"
on "airbyte".public."collaborators" using btree

It turns out IF NOT EXISTS was not in 9.4 but was in the 9.5 version.

Note: I have not actually tested on 9.5, but I do know 9.4 doesn't work.

How

Update documentation

🚨 User Impact 🚨

No functionality impact.

[CLAassistant]

All committers have signed the CLA.

[marcosmarxm]

thanks @bleonard https://dba.stackexchange.com/questions/35616/create-index-if-it-does-not-exist