Fix rack deprecation warning #262

Job	Run time
build (2.5.3, gemfiles/rails50.gemfile)	57s
build (2.5.3, gemfiles/rails51.gemfile)	57s
build (2.5.3, gemfiles/rails52.gemfile)	1m 0s
build (2.5.3, gemfiles/rails60.gemfile)	1m 57s
build (2.5.3, gemfiles/rails61.gemfile)	2m 7s
build (2.6.0, gemfiles/rails50.gemfile)	1m 0s
build (2.6.0, gemfiles/rails51.gemfile)	56s
build (2.6.0, gemfiles/rails52.gemfile)	1m 2s
build (2.6.0, gemfiles/rails60.gemfile)	2m 20s
build (2.6.0, gemfiles/rails61.gemfile)	2m 12s
build (2.6.6, gemfiles/rails50.gemfile)	1m 1s
build (2.6.6, gemfiles/rails51.gemfile)	57s
build (2.6.6, gemfiles/rails52.gemfile)	1m 10s
build (2.6.6, gemfiles/rails60.gemfile)	2m 6s
build (2.6.6, gemfiles/rails61.gemfile)	2m 0s
build (2.7.2, gemfiles/rails50.gemfile)	59s
build (2.7.2, gemfiles/rails51.gemfile)	56s
build (2.7.2, gemfiles/rails52.gemfile)	1m 10s
build (2.7.2, gemfiles/rails60.gemfile)	1m 2s
build (2.7.2, gemfiles/rails61.gemfile)	54s
build (gemfiles/rails71.gemfile, 3.2.2)	44s
build (gemfiles/rails71.gemfile, 3.1.1)	50s
build (gemfiles/rails70.gemfile, 3.1.1)	44s
build (gemfiles/rails70.gemfile, 3.0.3)	39s
build (gemfiles/rails61.gemfile, 3.0.3)	39s
	30m 19s

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