Remove Gemfile.lock and updated Gemfile dependancies

As the instructions want us to run bundle install which creates our Gemfile.lock file, including it only causes issues when updating gems.

Changed Gemfile to use https rather than http. There is no reason not to use https.

Gemfile dependencies updated to latest versions of gems.
Please note that jekyll needs to be updated at rubygems.org to remove a fixed dependency. Without this the build will fail. This change has been approved so wait for a few days for it to be updated before pushing.