use the rubocop gemfile for script/rlint

instead of an inline gemfile. this ensures the same lockfile is used as well

Change-Id: I885c6af20950ca331992e3ba0a0c06ef5ec673d5
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/327177
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Isaac Moore <isaac.moore@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>

script/rlint

@@ -3,14 +3,12 @@
 
 exit 0 if ENV["DISABLE_RUBOCOP"] == "1"
 
-require "bundler/inline"
+ENV["BUNDLE_GEMFILE"] = File.expand_path("../Gemfile.d/rubocop.rb", __dir__)
 
-gemfile do
-  source "https://rubygems.org/"
+require "rubygems"
+require "bundler/setup"
 
-  gem "gergich", "2.1.2"
-  gem "colorize", "0.8.1"
-end
+Bundler.setup
 
 require_relative "linter"
 require "optparse"