Handle case where mockgen is not installed

dev/up

@@ -8,7 +8,7 @@ if ! which golangci-lint &>/dev/null; then brew install golangci-lint; fi
 if ! which shellcheck &>/dev/null; then brew install shellcheck; fi
 if ! which protoc &>/dev/null; then brew install protobuf; fi
 if ! which protoc-gen-go &>/dev/null; then go install google.golang.org/protobuf/cmd/protoc-gen-go@latest; fi
-if [ `mockgen --version` != "v0.4.0" ]; then go install go.uber.org/mock/[email protected]; fi
+if ! which mockgen &>/dev/null || [ `mockgen --version` != "v0.4.0" ]; then go install go.uber.org/mock/[email protected]; fi
 if ! which protolint &>/dev/null; then go install github.com/yoheimuta/protolint/cmd/protolint@latest; fi
 
 dev/generate