title: Lacinia and re-graph incompatible headers
body: <p>I'm using the last available lacinia version: "0.36.0-alpha-3" with Luminus (Ring+reitit), but this version asks for a specific header:</p>
  
  <pre><code>$ curl 'http://localhost:3000/api/graphql' -X POST --data "{test_by_id(id: 5) { title } }" -H 'Content-Type: application/graphql'
  </code></pre>
  
  <p>that request works fine, but without "'Content-Type: application/graphql'" the request wouldn't work. So I need to define my re-graph init vector like:</p>
  
  <pre><code>  [::re-graph/init
      {:ws-url                  nil 
       :http-url                "http://localhost:3000/api/graphql"
       :http-parameters         {:with-credentials? false
                                 :headers {"Content-Type" "application/graphql"}
                                 }
       :ws-reconnect-timeout    nil
       :resume-subscriptions?   false   
       :connection-init-payload {}}]
  </code></pre>
  
  <p>but putting that header makes re-graph unable to work properly:</p>
  
  <pre><code>{"errors":[{"message":"Failed to parse GraphQL query.","extensions":{"errors":[{"locations":[{"line":1,"column":null}],"message":"mismatched input '\"query\"' expecting {'query', 'mutation', 'subscription', 
  </code></pre>
  
  <p>it looks like re-graph sends and receives data using "application/json" header, so lacinia asks for some type of header but re-graph can't work with that option.</p>