Remove JSON dependency

[DannyBen]

Why are you requiring the json gem as a dependency? It comes native with Ruby, and having it as a gem only causes conflicts and errors.

When I have rails_real_favicon installed (along with the json dependency it brings), in some other projects, I am getting JSON errors like the below.

/usr/share/rvm/rubies/ruby-2.7.0/lib/ruby/2.7.0/json/version.rb:4: warning: already initialized constant JSON::VERSION
/store/gems/ruby-2.7.0/gems/json-2.3.1/lib/json/version.rb:4: warning: previous definition of VERSION was here

I think you should simply remove it from the gemspec.
In cases when JSON is not bundled natively with Ruby (for example on Alpine linux), people can install it either as a gem or as a native OS package.