Use Capybara waiting for URL tests

Hopefully this fixes that nasty flaky failure for good!

tests/spec/support/matchers/be_at_url.rb

@@ -1,11 +1,19 @@
+class NotAtUrlError < StandardError; end
+
 RSpec::Matchers.define :be_at_url do |path, query = {}|
   match do |page|
-    uri = URI::parse(page.current_url)
-    expect(uri.path).to eql(path)
+    page.document.synchronize(nil, errors: [NotAtUrlError] ) do
+      uri = URI::parse(page.current_url)
+      raise NotAtUrlError unless uri.path == path
+
+      query = query.map { |k, v| [k.to_s, Array(v).map(&:to_s)] }.to_h
+      query_hash = CGI::parse(uri.query || '')
+      raise NotAtUrlError unless query <= query_hash
 
-    query = query.map { |k, v| [k.to_s, Array(v).map(&:to_s)] }.to_h
-    query_hash = CGI::parse(uri.query || '')
-    expect(query_hash).to include(query)
+      true
+    end
+  rescue NotAtUrlError
+    false
   end
 
   failure_message do |page|