[dmd-internals] Correction to name mangling doc

[Trass3r]

> Svn 370. Which I think was a really bad idea. The i should always be
> there, for any positive number. It's a fantasy to think that the ABI
> is stable at this point (eg, bug 3398 "Attributes inside a union
> screws data alignment" has only just been fixed). We could fix all
> remaining ABI issues in one go, then declare it stable.

So is this going to be reverted?