Log Message:
grpc: update to 1.31.1.

This release is a patch specifically for the Ruby bindings, which adds two \ 
backported PRs:

    Backport "Ruby: use absolute module name for request/response \ 
namespaces" to 1.31.x (#23830)
    Backport "Copy channel args hash before appending ruby user agent" \ 
to 1.31.x (#23826)