Fix ActionMailer plugin to add `rescue_from` to the correct class (#1… #269

Job	Run time
build (2.5.3, gemfiles/rails50.gemfile)	1m 3s
build (2.5.3, gemfiles/rails51.gemfile)	1m 5s
build (2.5.3, gemfiles/rails52.gemfile)	1m 5s
build (2.5.3, gemfiles/rails60.gemfile)	1m 58s
build (2.5.3, gemfiles/rails61.gemfile)	2m 17s
build (2.6.0, gemfiles/rails50.gemfile)	1m 5s
build (2.6.0, gemfiles/rails51.gemfile)	1m 4s
build (2.6.0, gemfiles/rails52.gemfile)	1m 5s
build (2.6.0, gemfiles/rails60.gemfile)	2m 3s
build (2.6.0, gemfiles/rails61.gemfile)	1m 59s
build (2.6.6, gemfiles/rails50.gemfile)	1m 9s
build (2.6.6, gemfiles/rails51.gemfile)	1m 1s
build (2.6.6, gemfiles/rails52.gemfile)	1m 3s
build (2.6.6, gemfiles/rails60.gemfile)	2m 2s
build (2.6.6, gemfiles/rails61.gemfile)	1m 57s
build (2.7.2, gemfiles/rails50.gemfile)	1m 2s
build (2.7.2, gemfiles/rails51.gemfile)	56s
build (2.7.2, gemfiles/rails52.gemfile)	1m 10s
build (2.7.2, gemfiles/rails60.gemfile)	2m 5s
build (2.7.2, gemfiles/rails61.gemfile)	2m 7s
build (gemfiles/rails71.gemfile, 3.2.2)	50s
build (gemfiles/rails71.gemfile, 3.1.1)	43s
build (gemfiles/rails70.gemfile, 3.1.1)	49s
build (gemfiles/rails70.gemfile, 3.0.3)	44s
build (gemfiles/rails61.gemfile, 3.0.3)	39s
	33m 1s

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