Fix HHVM issue with Ubuntu Xenial

Author: iam404

ee/cli/plugins/stack.py

@@ -739,7 +739,8 @@ def post_pref(self, apt_packages, packages):
 
                 EEFileUtils.searchreplace(self, "/etc/hhvm/server.ini",
                                                 "9000", "8000")
-                EEFileUtils.searchreplace(self, "/etc/nginx/hhvm.conf",
+                if not EEVariables.ee_platform_codename == 'xenial':
+                    EEFileUtils.searchreplace(self, "/etc/nginx/hhvm.conf",
                                                 "9000", "8000")
 
                 with open("/etc/hhvm/php.ini", "a") as hhvm_file: