Bug with --only and -only_recursion_depth

[lucascarrias]

What:

An exception is raised when you provide a single model name with --only and --only_recursion_depth

Step to reproduce:

At the CLI, enter --only with just one model name, then provide --only_recursion_depth with any valid integer.

Example:
erd --only ModelName --only_recursion_depth=1

Debug:

rails-erd 1.6.1

Failed: NoMethodError: undefined method `each' for "ModelName":String
    from /home/ruby/2.7.5/lib/ruby/gems/2.7.0/gems/rails-erd-1.6.1/lib/rails_erd/diagram.rb:129:in `generate'
    from /home/ruby/2.7.5/lib/ruby/gems/2.7.0/gems/rails-erd-1.6.1/lib/rails_erd/diagram.rb:119:in `create'
    from /home/ruby/2.7.5/lib/ruby/gems/2.7.0/gems/rails-erd-1.6.1/lib/rails_erd/diagram.rb:74:in `create'
    from /home/ruby/2.7.5/lib/ruby/gems/2.7.0/gems/rails-erd-1.6.1/lib/rails_erd/cli.rb:193:in `create_diagram'
    from /home/ruby/2.7.5/lib/ruby/gems/2.7.0/gems/rails-erd-1.6.1/lib/rails_erd/cli.rb:167:in `start'
    from /home/ruby/2.7.5/lib/ruby/gems/2.7.0/gems/rails-erd-1.6.1/lib/rails_erd/cli.rb:156:in `start'
    from /home/ruby/2.7.5/lib/ruby/gems/2.7.0/gems/rails-erd-1.6.1/bin/erd:4

Possible fix:

Make sure that options[:only] is always an array

rails-erd/lib/rails_erd/diagram.rb

Lines 129 to 132 in e41243f

	options[:only].dup.each do |class_name|
	options[:only]+= recurse_into_relationships(@domain.entity_by_name(class_name), depth)
	end
	options[:only].uniq!