Revert "increase pool max_size"
Revert "increase pool max_size"

This reverts commit 362a5a3c2f7f7253f92ca48fcfa81daddfeeb959.

rust-rethinkdb/reql,rust-rethinkdb/reql,rust-rethinkdb/reql,rust-rethinkdb/reql,rust-rethinkdb/reql,rust-rethinkdb/reql