rpc: Change append(foo, bar...) to copy(foo, bar) (#227)
rpc: Change append(foo, bar...) to copy(foo, bar) (#227)

As per
https://github.com/yarpc/yarpc-go/pull/225/files/8c848e022b50a3c5d46c4980b28f5a61f5269fa1#r67798985
yarpc/yarpc-go,yarpc/yarpc-go