Set meta referrer=origin (#412)

GraphQL query can be huge. And once encoded in the URL, it generates an enormous HTTP header "Referrer" that some HTTP servers cannot handle.

src/renderGraphiQL.js

@@ -55,6 +55,7 @@ add "&raw" to the end of the URL within a browser.
   <meta charset="utf-8" />
   <title>GraphiQL</title>
   <meta name="robots" content="noindex" />
+  <meta name="referrer" content="origin">
   <style>
     html, body {
       height: 100%;