Add github pull request as reference

Author: jvazquez-r7

modules/exploits/multi/http/x7chat2_php_exec.rb

@@ -26,6 +26,11 @@ def initialize(info = {})
           'Fernando Munoz <fernando[at]null-life.com>', # discovery & module development
           'Juan Escobar <eng.jescobar[at]gmail.com>', # module development @itsecurityco
         ],
+      'References'     =>
+        [
+          # Using this URL because isn't nothing else atm
+          ['URL', 'https://github.com/rapid7/metasploit-framework/pull/4076']
+        ],
       'Platform'       => 'php',
       'Arch'           => ARCH_PHP,
       'Targets'        => [['Generic (PHP Payload)', {}]],