#401 update to Ruby 2.5.1

[Aliciawyse]

I updated the Ruby version to 2.5.1.

FYI, I got this error when I ran gem install bundler:

error: While executing gem ... (Gem::FilePermissionError). I googled around and noticed I could fix it by adding the following line eval "$(rbenv init -)" to my .bash_profile file. Everything ran as expected after that. The tests pass!

[siliconmeadow]

Environment: Manjaro (up-to-date) with 5.4 kernel + rvm 1.29.8

I've verified this works.

As this PR is 18 months old, I also tried it with 2.6.3 (which was recommended via RVM). I think it's important to consider making it a policy to stick with the stable releases, as mentioned here:

http://www.ruby-lang.org/en/downloads/

Notice that 2.2.1 (as per the requirements of gh-pages branch) is not mentioned anywhere. If I use 2.2.1, I get the following error with gem install bundler :

$ gem install bundler
ERROR:  Error installing bundler:
	The last version of bundler (>= 0) to support your Ruby & RubyGems was 1.17.3. Try installing it with `gem install bundler -v 1.17.3`
	bundler requires Ruby version >= 2.3.0. The current ruby version is 2.2.1.85.

If I do a gem install bundler -v 1.17.3 I get further, but trying to start Jekyll with bundle exec jekyll serve --watch gives me this ugly error:

bundle exec jekyll serve --watch                                              ✔  10108  21:34:50
/home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/em-websocket-0.5.1/lib/em-websocket/masking04.rb:3:in `<module:WebSocket>': superclass must be a Class (Class given) (TypeError)
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/em-websocket-0.5.1/lib/em-websocket/masking04.rb:2:in `<module:EventMachine>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/em-websocket-0.5.1/lib/em-websocket/masking04.rb:1:in `<top (required)>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/em-websocket-0.5.1/lib/em-websocket.rb:15:in `require'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/em-websocket-0.5.1/lib/em-websocket.rb:15:in `block in <top (required)>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/em-websocket-0.5.1/lib/em-websocket.rb:14:in `each'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/em-websocket-0.5.1/lib/em-websocket.rb:14:in `<top (required)>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/jekyll-livereload-0.2.2/lib/jekyll-livereload/websocket.rb:28:in `require'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/jekyll-livereload-0.2.2/lib/jekyll-livereload/websocket.rb:28:in `<top (required)>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/jekyll-livereload-0.2.2/lib/jekyll-livereload.rb:18:in `require'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/jekyll-livereload-0.2.2/lib/jekyll-livereload.rb:18:in `<module:Livereload>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/jekyll-livereload-0.2.2/lib/jekyll-livereload.rb:4:in `<module:Jekyll>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/jekyll-livereload-0.2.2/lib/jekyll-livereload.rb:3:in `<top (required)>'
	from /home/rsheppard/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/bundler/runtime.rb:81:in `require'
	from /home/rsheppard/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/bundler/runtime.rb:81:in `block (2 levels) in require'
	from /home/rsheppard/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/bundler/runtime.rb:76:in `each'
	from /home/rsheppard/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/bundler/runtime.rb:76:in `block in require'
	from /home/rsheppard/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/bundler/runtime.rb:65:in `each'
	from /home/rsheppard/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/bundler/runtime.rb:65:in `require'
	from /home/rsheppard/.rvm/rubies/ruby-2.2.1/lib/ruby/site_ruby/2.2.0/bundler.rb:114:in `require'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/jekyll-3.6.3/lib/jekyll/plugin_manager.rb:51:in `require_from_bundler'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/gems/jekyll-3.6.3/exe/jekyll:11:in `<top (required)>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/bin/jekyll:23:in `load'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/bin/jekyll:23:in `<main>'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/bin/ruby_executable_hooks:24:in `eval'
	from /home/rsheppard/.rvm/gems/ruby-2.2.1@codebar-tutorial/bin/ruby_executable_hooks:24:in `<main>'```