Set no-follow-redirects local instead of global

When setting no-follow-redirects for RequestBuilder#getRedirectUrl()
(e.g., avatar requests), do so only for this one request. Previously, it
was set globally for all requests, then set back to its initial state
after the request completed. This should prevent multithreading issues
where numerous threads are attempting to alter the global state of
HttpURLConnection#setFollowRedirects().

Fixes #94

src/main/java/com/tumblr/jumblr/request/RequestBuilder.java

@@ -40,10 +40,8 @@ public RequestBuilder(JumblrClient client) {
     public String getRedirectUrl(String path) {
         OAuthRequest request = this.constructGet(path, null);
         sign(request);
-        boolean presetVal = HttpURLConnection.getFollowRedirects();
-        HttpURLConnection.setFollowRedirects(false);
+        request.setFollowRedirects(false);
         Response response = request.send();
-        HttpURLConnection.setFollowRedirects(presetVal);
         if (response.getCode() == 301) {
             return response.getHeader("Location");
         } else {