Use the defined type to the default value of directory

Currently, you will get Thor's deprecated message when starting the `Listen::CLI`.

```
Deprecation warning: Expected array default value for '--directory'; got "." (string).
This will be rejected in the future unless you explicitly pass the options `check_default_type: false` or call `allow_incompatible_default_type!` in your code
You can silence deprecations warning by setting the environment variable THOR_SILENCE_DEPRECATION.
```

This is due to the incorrect default value(`directory` is defined as an `array`,
but the default value is a `string`).

This fixed to use the correct default value and correctly pass to the `directory`
to `Listen.to`.

lib/listen/cli.rb

@@ -18,9 +18,9 @@ class CLI < Thor
 
     class_option :directory,
                  type:    :array,
-                 default: '.',
+                 default: ['.'],
                  aliases: '-d',
-                 banner:  'The directory to listen to'
+                 banner:  'One or more directories to listen to'
 
     class_option :relative,
                  type:    :boolean,
@@ -55,7 +55,7 @@ def start
         end
       end
 
-      listener = Listen.to(directory, relative: relative, &callback)
+      listener = Listen.to(*directory, relative: relative, &callback)
 
       listener.start
 

spec/lib/listen/cli_spec.rb

@@ -15,7 +15,7 @@
       let(:options) { %w[] }
       it 'is set to local directory' do
         expect(Listen::Forwarder).to receive(:new) do |options|
-          expect(options[:directory]).to eq('.')
+          expect(options[:directory]).to eq(['.'])
           forwarder
         end
         described_class.start(options)
@@ -108,7 +108,7 @@
   it 'passes relative option to Listen' do
     value = double('value')
     expect(Listen).to receive(:to).
-      with(nil, hash_including(relative: value)).
+      with(hash_including(relative: value)).
       and_return(listener)
 
     described_class.new(relative: value).start