added a warning about a security issue when using the _internal route
Merge branch '2.0' into 2.1

* 2.0:
  added a warning about a security issue when using the _internal route
updated VENDORS for 2.1.6
fixed 2.1.6 composer.lock file
Merge tag 'v2.1.6' into no-acme

created tag 2.1.6