title: How to create a map of strings from map[string]interface{}?
body: <p>Noob gopher here. 
  I'd like to fill data into this struct field:</p>
  
  <pre><code>userData map[string]interface{}
  </code></pre>
  
  <p>The data is like: </p>
  
  <pre><code>ud := map[string]string{"userName": "noob"}
  </code></pre>
  
  <p>but I get this comple time error:</p>
  
  <blockquote>
    <p>cannot use ud (type map[string]string) as type map[string]interface {}
    in field value</p>
  </blockquote>
  
  <p>I also tried:</p>
  
  <pre><code>ud := map[string]interface{"userName": "noob".(string)}
  </code></pre>
  
  <p>but this gives:</p>
  
  <blockquote>
    <p>syntax error: unexpected string literal</p>
  </blockquote>
  
  <p>How can I fix this?</p>