Add specs for hook commands.
user
```ruby
# encoding: utf-8

require 'spec_helper'

describe GithubCLI::Commands::Hooks do
  let(:format) { 'table' }
  let(:user)   { 'peter-murach' }
  let(:repo)   { 'github_cli' }
  let(:id)     { 1 }
  let(:api_class) { GithubCLI::Hook }

  it "invokes hook:list" do
    api_class.should_receive(:all).with(user, repo, {}, format)
    subject.invoke "hook:list", [user, repo]
  end

  it "invokes hook:get" do
    api_class.should_receive(:get).with(user, repo, id, {}, format)
    subject.invoke "hook:get", [user, repo, id]
  end

  it "invokes hook:create --name --config" do
    api_class.should_receive(:create).with(user, repo, {'name' => 'web',
      "config" => { :url => "http://example.com/webhook" } }, format)
    subject.invoke "hook:create", [user, repo], :name => 'web',
      :config => {:url => "http://example.com/webhook" }
  end

  it "invokes hook:edit --name --config" do
    api_class.should_receive(:edit).with(user, repo, id, {'name' => 'web',
      "config" => { :url => "http://example.com/webhook" } }, format)
    subject.invoke "hook:edit", [user, repo, id], :name => 'web',
      :config => {:url => "http://example.com/webhook" }
  end

  it "invokes hook:test" do
    api_class.should_receive(:test).with(user, repo, id, {}, format)
    subject.invoke "hook:test", [user, repo, id]
  end

  it "invokes hook:delete" do
    api_class.should_receive(:delete).with(user, repo, id, {}, format)
    subject.invoke "hook:delete", [user, repo, id]
  end
end
```
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