Store php version as PHP_VERSION environment variable

src/Handler.php

@@ -297,6 +297,7 @@ class Handler extends BaseHandler {
       $options['projectroot'] = $projectRoot;
 
       $this->options = $env->replaceEnvironmentVariables($options);
+      $env->put('PHP_VERSION', $this->options['php']['version'], TRUE);
     }
     if ($key !== NULL) {
       return $this->options[$key];