如何将PHP应用程序部署到Heroku？

Question

I have a legacy PHP application. The root directory looks like this:

.htaccess
index.php
composer.json
composer.lock
Procfile

In my procfile I have this:

web: vendor/bin/heroku-php-apache2 /

And in .htaccess:

RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [QSA,L]

And in composer.json this:

{
  "require" : {
    "silex/silex": "~1.1",
    "monolog/monolog": "~1.7"
  },
  "require-dev": {
    "heroku/heroku-buildpack-php": "*"
  }
}

When I deploy to heroku I get no errors, just a blank screen. I am unable to run the app locally with foreman due to it throwing this error:

This program requires Apache 2.4.10 or newer with mod_proxy 
and mod_proxy_fcgi enabled; check your 'httpd' command.

Additionally, I'm getting a 500 server error on the Heroku site.

I'm wondering if I am doing anything that is obviously wrong here. Not very experienced with deploying PHP applications on Heroku so I'm not sure exactly what the deal is. Thanks in advance for the help!