Switch OSS build to SAI 1.5
Switch OSS build to SAI 1.5

Summary:
We need to add a separate manifest for SAI 1.4 and build that too, but that is
for later diffs, for now, we need 1.5, so change it.

Differential Revision: D20019016

fbshipit-source-id: 8630340ac7c8b7d94e6b768a2efa96266b2cc3e0

rsocket/rsocket-cpp,ReactiveSocket/reactivesocket-cpp,ReactiveSocket/reactivesocket-cpp,ReactiveSocket/reactivesocket-cpp,rsocket/rsocket-cpp,rsocket/rsocket-cpp,rsocket/rsocket-cpp