Update Gemfile

Gemfile

 source "https://rubygems.org"
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-# Hello! This is where you manage which Jekyll version is used to run.
-# When you want to use a different version, change it below, save the
-# file and run `bundle install`. Run Jekyll with `bundle exec`, like so:
-#
-#     bundle exec jekyll serve
-#
-# This will help ensure the proper Jekyll version is running.
-# Happy Jekylling!
-gem "jekyll", "3.5.1"
-
-# This is the default theme for new Jekyll sites. You may change this to anything you like.
-gem "minima", "~> 2.0"
-
-# If you want to use GitHub Pages, remove the "gem "jekyll"" above and
-# uncomment the line below. To upgrade, run `bundle update github-pages`.
-# gem "github-pages", group: :jekyll_plugins
-
-# If you have any plugins, put them here!
-group :jekyll_plugins do
-   gem "jekyll-feed", "~> 0.6"
-end
-
-# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
-gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]
-