v1.5.2: Release api_core 1.5.2 (#6471)

11-09-2018 14:22 PST

Implementation Changes

• Retry transient errors in 'PollingFuture.result'. (#6305)

Dependencies

• Remove hyphen from named extra in api_core. (#6468)
• Bump minimum 'api_core' version for all GAPIC libs to 1.4.1. (#6391)
• Avoid broken 'google-common-apis 1.5.4' release. (#6355)