Please update grpc-gateway version to at least v2.1.0, better yet v2.4.0

[EraYaN]

This makes sure the format specifier for a field is supported (from the current "a bit of everything" grpc-gateway example).

Implemented here:
grpc-ecosystem/grpc-gateway#1841

Shipped in v2.1.0

I'd also take the latest v2.4.0, I tested with that and it does work without changing any of the other versions.

[jcburley]

Likely to be addressed by: #361