**Update - this answer is about adding `meta` to Visualforce pages, not lightning components as originally asked**

This seems to be a limitiation in Visualforce and Apex. Disclosure: I'm new to VF / Apex but very experienced in HTML. There are Apex-approved ways of adding scripts and stylesheets to the `head` of a document with the `<apex:includeScript />` and `<apex:stylesheet />` tags.

But there's no equivalent for adding `meta` as far as I know.

You can, as a type of hack, insert the `<meta ... >` at the top of the VF page and it may work. I've done a similar quick workaround with the `<meta viewport...>` element for responsive pages on mobile devices, and it works. 

However, this is technically invalid markup.

A related answer at https://salesforce.stackexchange.com/a/5412/27617 has more details about adding `meta`