Remove newline from test import paths.

When running "make test" on my machine, I got many unrecognized import
path errors, and the path showed a trailing "\n". Changing the go list
format to remove the newline fixed these.

Makefile

@@ -15,8 +15,7 @@ format:
 
 test:
 	@echo "$(OK_COLOR)==> Testing Packer...$(NO_COLOR)"
-	@go list -f '{{range .TestImports}}{{.}}\
-		{{end}}' ./... | xargs -n1 go get -d
+	@go list -f '{{range .TestImports}}{{.}} {{end}}' ./... | xargs -n1 go get -d
 	go test ./...
 
 .PHONY: all format test