Use relative paths for file header references

[jkrrv]

Resolves #383

[swissspidy]

Thanks for the fix!

Not sure why the test didn't catch this:

i18n-command/features/makepot.feature

Lines 69 to 101 in ca7a44a

	Scenario: Adds file references for file headers.
	Given an empty foo-plugin directory
	And a foo-plugin/foo-plugin.php file:
	"""
	<?php
	/**
	* Plugin Name: Foo Plugin
	* Plugin URI: https://example.com
	* Description: Plugin Description
	* Version: 0.1.0
	* Author:
	* Author URI:
	* License: GPL-2.0+
	* License URI: http://www.gnu.org/licenses/gpl-2.0.txt
	* Text Domain: foo-plugin
	* Domain Path: /languages
	*/
	"""
	When I try `wp i18n make-pot foo-plugin foo-plugin.pot`
	Then the foo-plugin.pot file should exist
	And the foo-plugin.pot file should contain:
	"""
	Description of the plugin
	"""
	And the foo-plugin.pot file should contain:
	"""
	#: foo-plugin.php
	"""
	And the foo-plugin.pot file should contain:
	"""
	Plugin Description
	"""

[jkrrv]

Awesome. Thanks for the speedy response.