v0.0.1: use "replace" directive to get the updated version of grpc-gateway

Removed the "vendor" directory since we have switched to the go modules.

Used "replace" directive to get rid of the warning when running pxc.

This gets rid of the warning about use of the deprecated "generator" package.

Signed-off-by: Neelesh Thakur <neelesh.thakur@purestorage.com>