Does not build on Windows 7

[bjartwolf]

Seems to be an issue with the JSON gem and SSL on Windows 7.

By manually hard-coding the github-pages version in the Gemfile to "96" I could run bundle install wihtout errors and start the site.

[!] There was an error parsing `Gemfile`: SSL_connect returned=1 errno=0 state=SSLv3 read server certificate B: certific
ate verify failed. Bundler cannot continue.

 #  from Z:/Documents/GitHub/sonic-pi-workshop/Gemfile:5
 #  -------------------------------------------
 #
 >  gem 'github-pages', versions['github-pages']
 #  source 'https://rubygems.org'
 #  -------------------------------------------