ENH Publish developer-docs before other modules

[emteknetnz]

Issue #253

Tested locally by creating a new fake release with DEV_MODE=1 in my .env file and adding echo("$name\n");return; to PublishRelease::releaseLibrary() to show the order that modules would be released in

Before:

silverstripe/assets
silverstripe/config
silverstripe/framework
...
silverstripe/developer-docs
...
silverstripe/recipe-kitchen-sink

After:

silverstripe/developer-docs
silverstripe/assets
silverstripe/config
silverstripe/framework
...
silverstripe/recipe-kitchen-sink

I've double checked that silverstripe/developer-docs only appears once in the "after" list

[GuySartorelli]

Seems like it should work just fine 👍