Update lessphp to b7cd5c79e8

Update lessphp to b7cd5c79e8

Source:
* https://github.com/leafo/lessphp/blob/b7cd5c79e8/lessc.inc.php
* https://github.com/leafo/lessphp/compare/261f1bd2...b7cd5c79e8

Updates:
 * 1d62556008: CS fixes
 * d3fd5cec9e: use the built-in php magic database instead of the system one
 * 34fdf60f32: data-uri: add tests and use lessc::findImport to locate the file
 * 72b25725d9: implement data-uri([mimetype,] url) from less.js 1.4.0
 * 5cf7eb272e: Update lessc.inc.php
 * 7e64e41a59: Fix color contrast and threshold calculation
 * 69adc23a92: Use property_exist to avoid "Undefined property: stdClass::$parent"

Change-Id: Ie626b4f1117b44669bd2c6c43a0186d95b36435a