Fix Programmatic subscription Go example (#3679)

Signed-off-by: Anton Troshin <anton@diagrid.io>
Co-authored-by: Mark Fussell <markfussell@gmail.com>

daprdocs/content/en/developing-applications/building-blocks/pubsub/subscription-methods.md

@@ -321,6 +321,7 @@ app.listen(port, () => console.log(`consumer app listening on port ${port}!`))
 ```go
 package main
 
+import (
 	"encoding/json"
 	"fmt"
 	"log"