fix infinite reload loop on login for WebKit browser

Summary

Using Vimb, a WebKit-based browser, attempts to sign in to GitLab.com result in an infinite "checking your browser" loop on a five-second timer. (This also occurs with Surf, another WebKit-based browser.)

Steps to reproduce

1. Open Vimb (a WebKit-based browser).
2. Navigate to a GitLab.com repository.
3. Click the "Sign in / Register" button at the top right.
4. Observe infinite loop behavior.

Example Project

This appears to occur with any GitLab.com hosted project.

What is the current bug behavior?

A page loads containing the GitLab logo and this text:

Checking your browser before accessing gitlab.com.

This process is automatic. Your browser will redirect to your requested content shortly.

Please allow up to 5 seconds…

This page reloads every five seconds.

What is the expected correct behavior?

GitLab.com should direct me to a login page.

Relevant logs and/or screenshots

Output of checks

This bug happens on GitLab.com.