v1.21.0

Features

• add support for CommitStats (#261) (b32e7ae)
• allow using UUID in PreparedStatement (#365) (4cbee6d), closes #364

Dependencies

• update dependency com.google.cloud:google-cloud-shared-dependencies to v0.20.1 (#384) (f0cdf11)
• update dependency com.google.cloud:google-cloud-spanner-bom to v5 (#386) (910c50c)