Fetching source Error

[hoyeong]

Fetching source index from https://rubygems.org/
Could not verify the SSL certificate for https://rubygems.org/.
There is a chance you are experiencing a man-in-the-middle attack, but most likely your system doesn't have the CA certificates needed for
verification. For information about OpenSSL certificates, see bit.ly/ruby-ssl. To connect without using SSL, edit your Gemfile sources and
change 'https' to 'http'.

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what they mean is at the top of the Gemfile in your rails application directory change
source 'https://rubygems.org'
to
source 'http://rubygems.org'