Use secure RubyGems source

Gemfile

-source "http://rubygems.org"
+source 'https://rubygems.org'
 
 group :development, :test do
   gem 'listen', '~> 0.5.0'

Gemfile.lock

 GEM
-  remote: http://rubygems.org/
+  remote: https://rubygems.org/
   specs:
     addressable (2.5.2)
       public_suffix (>= 2.0.2, < 4.0)