fix to accept array of strings to exact match of sequence of lines

This patch provides matcher to check whether the specified file contains specified lines exactly or not.

```ruby
describe file('/home/mizzy/.ssh/config') do
  ssh_conf_lines = (<<EOL).split(/\n/)
Host some.server.local
    User gosukenator
    IdentityFile ~/.ssh/id_rsa_mizzy
    Port 8022
    StrictHostKeyChecking yes
EOL
  it { should contain ssh_conf_lines }
```

Related with: https://github.com/serverspec/specinfra/pull/85