Make corgi docs optional

Author: iarna

lib/request.js

@@ -116,10 +116,12 @@ function makeRequest (uri, params, cb_) {
   var er = this.authify(params.authed, parsed, headers, params.auth)
   if (er) return cb_(er)
 
+  var useCorgi = params.corgi == null ? true : params.corgi
+
   var opts = this.initialize(
     parsed,
     params.method,
-    'application/vnd.npm.install-v1+json; q=1.0, application/json; q=0.8, */*',
+    corgi ? 'application/vnd.npm.install-v1+json; q=1.0, application/json; q=0.8, */*' : 'application/json',
     headers
   )