Add Post Deploy-Hook as HTTP POST Notification for deployhq.com deploys. Put the following file in the root directory of your project or adjust the path in line 24.

hook.php

<?PHP
$publicKey = "-----BEGIN PUBLIC KEY-----
MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDXJcP2N6NtcN26Q8nVaidXOA0w 
RxWK2HQTblIaQdGRDjqTvhrSlFuV5N4jz7w/w8uskP20G7ZQ+CkHwIXrWk76KZJn 
pdoOHPO6AqRmEFgV5Q6Y1CR77mvnT9O21hTnfzfyyiAdQC2oO8M9/jeLRPTAqmkG 
xdQa8iepUz4BwrrHmwIDAQAB 
-----END PUBLIC KEY-----";

// Verify integrity of Payload
$result = openssl_verify($_POST['payload'], base64_decode($_POST['signature']), $publicKey);

if($result && $_SERVER['CONTENT_TYPE'] == "application/x-www-form-urlencoded"){
    $json = stripslashes($_POST['payload']);
    $payload = json_decode($json);

    if($payload->status == "completed"){

        // Get changed files:
        $SID = $payload->servers[0]->identifier;
        $ChangedFiles = $payload->files->$SID->changed;

        // Minify changed files:
        if(is_array($ChangedFiles))
            minify($ChangedFiles);
    }
}


/*
 * JS and CSS Minifier 
 * version: 1.0 (2013-08-26)
 *
 * This document is licensed as free software under the terms of the
 * MIT License: http://www.opensource.org/licenses/mit-license.php
 *
 * Toni Almeida wrote this plugin, which proclaims:
 * "NO WARRANTY EXPRESSED OR IMPLIED. USE AT YOUR OWN RISK."
 * 
 * This plugin uses online webservices from javascript-minifier.com and cssminifier.com
 * This services are property of Andy Chilton, http://chilts.org/
 *
 * Copyrighted 2013 by Toni Almeida, promatik.
 *
 * Edited 2015 by Michael Lorer, 01-Scripts.de
 */
function minify($arr, $addpath="") {
    foreach ($arr as $file) {
        $file = $addpath.$file;
        switch(FileExtension($file)){
            case "css":
              $url = "http://cssminifier.com/raw";
              break;
            case "js":
              $url = "http://javascript-minifier.com/raw";
              break;
            default:
              $url = "";
        }

        if(empty($url)) continue;

        $handler = fopen($file, 'r+');
        if(!$handler) continue;

        $content = file_get_contents($file);
        ftruncate($handler, 0);
        fwrite($handler, getMinified($url, $content));
        fclose($handler);
        echo "File <a href='" . $file . "'>" . $file . "</a> done!<br />";
    }
}

function getMinified($url, $content) {
    $postdata = array('http' => array(
        'method'  => 'POST',
        'header'  => 'Content-type: application/x-www-form-urlencoded',
        'content' => http_build_query( array('input' => $content) ) ) );
    return file_get_contents($url, false, stream_context_create($postdata));
}

function FileExtension($filestring){
    if(empty($filestring)) return "";

    $pathinfo = pathinfo($filestring);
    return strtolower($pathinfo['extension']);
}
?>