title: Swagger generation is ignoring SecurityDefiniton
body: <p>Cannot understand one thing, why <code>swag init</code> command is generating everything, except <code>SecurityDefinition</code> block</p>
  <p>For example, this is my code on main function:</p>
  <pre><code>// @title Swagger API
  // @version 1.0
  // @description This is a documentation for PlatOps Core tool.
  // @termsOfService http://platops.com/
  // @license.name Apache 2.0
  // @license.url http://www.apache.org/licenses/LICENSE-2.0.html
  // @host test.com
  // @BasePath /v2
  // @securityDefinitions.apikey Bearer
  // @in header
  // @name Authorization
  </code></pre>
  <p>And how I'm using :</p>
  <pre><code>// GetUser godoc
  // @Summary Retrieves users list
  // @Tags users
  // @Accept json
  // @Produce json
  // @Success 200 {object} string
  // @Failure 400,404 {object} string
  // @Failure 500 {object} string
  // @Router /api/users/ [get]
  // @Security Bearer
  </code></pre>
  <p>From this, it's generating everything, this path also, but no SecurityDefinition block inside.</p>
  <p>I'm trying to implement this one:
  <a href="https://github.com/swaggo/swag#security" rel="nofollow noreferrer">https://github.com/swaggo/swag#security</a></p>
  <p>P.S. If I put already generated text on the generated doc file, it's working... so why it cannot generate it?</p>
  <pre><code>&quot;securityDefinitions&quot;: {
          &quot;api_key&quot;: {
              &quot;type&quot;: &quot;apiKey&quot;,
              &quot;name&quot;: &quot;Bearer&quot;,
              &quot;in&quot;: &quot;header&quot;
          },
  }
  </code></pre>