Bump rack gem to 2.0.7

This update has two important fixes:

1. It reverts the monkey patch introduced in
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/23385 since
https://github.com/rack/rack/pull/1201 is now part of the release.

2. Preserve forwarded IP address for trusted proxy chains
(https://github.com/rack/rack/pull/1343).

Gemfile

@@ -139,10 +139,7 @@ gem 'icalendar'
 gem 'diffy', '~> 3.1.0'
 
 # Application server
-# The 2.0.6 version of rack requires monkeypatch to be present in
-# `config.ru`. This can be removed once a new update for Rack
-# is available that contains https://github.com/rack/rack/pull/1201.
-gem 'rack', '2.0.6'
+gem 'rack', '~> 2.0.7'
 
 group :unicorn do
   gem 'unicorn', '~> 5.4.1'

Gemfile.lock

@@ -617,7 +617,7 @@ GEM
       puma (>= 2.7, < 4)
     pyu-ruby-sasl (0.0.3.3)
     raabro (1.1.6)
-    rack (2.0.6)
+    rack (2.0.7)
     rack-accept (0.4.5)
       rack (>= 0.4)
     rack-attack (4.4.1)
@@ -1100,7 +1100,7 @@ DEPENDENCIES
   pry-rails (~> 0.3.4)
   puma (~> 3.12)
   puma_worker_killer
-  rack (= 2.0.6)
+  rack (~> 2.0.7)
   rack-attack (~> 4.4.1)
   rack-cors (~> 1.0.0)
   rack-oauth2 (~> 1.9.3)

config.ru

@@ -13,10 +13,6 @@ if defined?(Unicorn)
     # Max memory size (RSS) per worker
     use Unicorn::WorkerKiller::Oom, min, max
   end
-
-  # Monkey patch for fixing Rack 2.0.6 bug:
-  # https://gitlab.com/gitlab-org/gitlab-ee/issues/8539
-  Unicorn::StreamInput.send(:public, :eof?) # rubocop:disable GitlabSecurity/PublicSend
 end
 
 require ::File.expand_path('../config/environment', __FILE__)