fix(proto): Fix broken regen-proto script

[ttomsu]

The only change I made was removing the -u in the regen-protos.sh script.

Here is the error it was generating:

build github.com/mitchellh/protoc-gen-go-json: cannot load github.com/grpc-ecosystem/grpc-gateway/codegenerator: module github.com/grpc-ecosystem/grpc-gateway@latest (v1.14.2) found, but does not contain package github.com/grpc-ecosystem/grpc-gateway/codegenerator

This looks to be an error introduced by a transitive dependency.

From the docs:

The -u flag instructs get to update modules providing dependencies
of packages named on the command line to use newer minor or patch
releases when available. 

With the -u flag, it was upgrading grpc-gateway (a transitive dependency) to v1.14 (a minor version bump) that apparently removed a required package, and thus was actually a breaking change. Sigh...semver is hard.