Correct viewport meta tag syntax

Fixes #1073. Brings meta tags into more complete compliance with [the 2013 CSS Device Adaptation draft](https://developer.mozilla.org/en-US/docs/Mozilla/Mobile/Viewport_meta_tag). In this case:

* delimiters are changed to commas, which is not required but preferred
* negative indication is "no," not "0"
* there is no trailing delimiter

This commit does not alter the UX or mobile display at all - it is purely a standards-compliance-motivated change.