host_name or host is required not both

[nelsonwittwer]

Description

Fixes shopify_app #1542 reported issue where new installs were breaking due to still requiring host_name when host was present.

host is the preferred and new default configuration option to make locahost the default

Adds pry-byebug as dev dependency to make debugging easier

How has this been tested?

New app install with localhost

1. Created a new Rails app with the latest version of shopify_app and ran the install generator.
2. In that new app, added gem "shopify_api", path: "../shopify-api-ruby" to my Gemfile and ran bundle install
3. Added HOST and API keys as ENV variables
4. booted server and verified I wasn't seeing the same required host_name error being thrown as the reported in issue

using a tunnel and only host_name config

1. Updated existing app that was using the host_name context setup attribute instead of ENV variable. This app also uses a tunnel to get TLS on local dev
2. In that new app, added gem "shopify_api", path: "../shopify-api-ruby" to my Gemfile and ran bundle install
3. booted server and verified it wasn't throwing an error
4. Was able to view embedded app without any exceptions

Checklist:

• My commit message follow the pattern described in here
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the project documentation.
• I have added a changelog line.