Add gemfile so we caan use bundler to install dependencies

9 jobs for master in 5 minutes and 56 seconds (queued for 1 second)
Status Job ID Name Coverage
  Syntax
passed #5646
jruby_1.7

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passed #5647
jruby_9.1

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passed #5640
ruby_2.1

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passed #5641
ruby_2.2

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passed #5642
ruby_2.3

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passed #5643
ruby_2.4

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passed #5644
ruby_2.5

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passed #5645
ruby_2.6

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passed #5648
rubocop

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