Add option for request retries

[gr2m]

I'm using this library to de-reference a JSON API spec with hundreds of references.

await jsonSchemaRefParser.dereference(
  "https://raw.githubusercontent.com/octokit/routes/v21.0.4/openapi/api.github.com/index.json"
);

I see random request errors which I could workaround quite easily by adding a simple retry feature in lib/resolvers/http.js

-    req.on("error", reject)
+    let retries = 3
+    req.on("error", error => {
+      if (!--retries) {
+        return reject(error);
+      }
+
+      console.log(`retrying GET ${u.href} (${3 - retries}/3)`);
+
+      return get(u, httpOptions).then(resolve, reject);
+    });

Instead of hardcoding it, it would be simple enough to add an option such as resolve.http.retries.

Would you accept a PR to add such an option?