add bundler setup requirement

[JensTimmerman]

this is needed to make whatweb work after following the installation instructions.

The current installation instructions for manual install tel me to

git clone repo cd WhatWeb bundle install -> Your user account isn't allowed to install to the system RubyGems. You can cancel this installation and run:

  bundle config set --local path 'vendor/bundle'
  bundle install

So I run bundle config set --local path 'vendor/bundle' bundle install -> Bundle complete! 11 Gemfile dependencies, 28 gems now installed. Bundled gems are installed into ./vendor/bundle

./whatweb
WhatWeb is not installed and is missing dependencies. The following gems are missing:

• addressable

To install run the following command from the WhatWeb folder: 'bundle install'

running bundle exec whatweb does work ruby -rbundler/setup whatweb also works

And so this patch also works.