title: multiple-value json.Marshal() in single-value context
body: <p><a href="https://play.golang.org/p/8MWR8-AeD9" rel="noreferrer">Here</a> you can see this code:</p>
  
  <pre><code>package main
  
  import (
      "fmt"
      "encoding/json"
  )
  
  func main() {
      map1 := map[string]map[string]interface{}{}
      map2 := map[string]interface{}{}
      map2["map2item"] = "map2item"
      map1["map2"] = map2
      fmt.Println(string(json.Marshal(map1)))
  }
  </code></pre>
  
  <p>that returns this error:</p>
  
  <pre><code>tmp/sandbox100532722/main.go:13:33: multiple-value json.Marshal() in single-value context.
  </code></pre>
  
  <p>How do I fix this?</p>