CBLT-268:  instantiated tokens @PRODUCT_VERSION@, @COMMIT_SHA@ before build

see couchbase-lite-ios commit:  ee5212dd5c79c0e40587a55659478d5eb621d01d

Change-Id: Ieae27afe15a9ebeac249b66481d739a84133244f
Reviewed-on: http://review.couchbase.org/35710
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>