Dependencies

• Remove Go 1.9 support; assume go1.12 build tag (#3767)

New Features

• grpc: add ServiceRegistrar interface; bump up support package version. (#3816; #3818)
• xds: add LRS balancing policy (#3799)

Bug Fixes

• server: prevent hang in Go HTTP transport in some error cases (#3833)
• server: respond correctly to client headers with END_STREAM flag set (#3803)
• eds: fix priority timeout failure when EDS removes all priorities (#3830)