make generate produces an error on MacOS

[David Klassen]

 ~/go/src/github.com/davidklassen/grpc-example/ master make generate
# Generate gogo, gRPC-Gateway, swagger, go-validators output.
#
# -I declares import folders, in order of importance
# This is how proto resolves the protofile imports.
# It will check for the protofile relative to each of these
# folders and use the first one it finds.
#
# --gogo_out generates GoGo Protobuf output with gRPC plugin enabled.
# --grpc-gateway_out generates gRPC-Gateway output.
# --swagger_out generates an OpenAPI 2.0 specification for our gRPC-Gateway endpoints.
# --govalidators_out generates Go validation files for our messages types, if specified.
#
# The lines starting with Mgoogle/... are proto import replacements,
# which cause the generated file to import the specified packages
# instead of the go_package's declared by the imported protof files.
#
# $GOPATH/src is the output directory. It is relative to the GOPATH/src directory
# since we've specified a go_package option relative to that directory.
#
# proto/example.proto is the location of the protofile we use.
protoc \
		-I proto \
		-I vendor/github.com/grpc-ecosystem/grpc-gateway/ \
		-I vendor/github.com/gogo/googleapis/ \
		-I vendor/ \
		--gogo_out=plugins=grpc,\
Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/duration.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types,\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api,\
Mgoogle/protobuf/field_mask.proto=github.com/gogo/protobuf/types:\
$GOPATH/src/ \
		--grpc-gateway_out=\
Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/duration.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types,\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api,\
Mgoogle/protobuf/field_mask.proto=github.com/gogo/protobuf/types:\
$GOPATH/src/ \
		--swagger_out=third_party/OpenAPI/ \
		--govalidators_out=gogoimport=true,\
Mgoogle/protobuf/timestamp.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/duration.proto=github.com/gogo/protobuf/types,\
Mgoogle/protobuf/empty.proto=github.com/gogo/protobuf/types,\
Mgoogle/api/annotations.proto=github.com/gogo/googleapis/google/api,\
Mgoogle/protobuf/field_mask.proto=github.com/gogo/protobuf/types:\
$GOPATH/src \
		proto/example.proto
# Workaround for https://github.com/grpc-ecosystem/grpc-gateway/issues/229.
sed -i "s/empty.Empty/types.Empty/g" proto/example.pb.gw.go
sed: 1: "proto/example.pb.gw.go": extra characters at the end of p command
make: *** [generate] Error 1