Add rubygem-google-cloud-spanner 1.11.0

Google Cloud Spanner API (docs) provides a fully managed, mission-critical,
relational database service that offers transactional consistency at global
scale, schemas, SQL (ANSI 2011 with extensions), and automatic, synchronous
replication for high availability.

WWW: https://github.com/googleapis/google-cloud-ruby/tree/master/google-cloud-spanner