Use comma instead of semicolon to separate k/v-pairs in viewport meta

While a draft "standard" of the CSS Working Group of the W3C (as
much as any W3C "living document" is a "standard" in any meaning of
the word) says in a (non normative) section that both semicolon and
comma are allowed [1], the MDN has the following thing to say [2]:

> To mitigate this problem of virtual viewport […], Apple introduced
> the "viewport meta tag" […]. Apple's documentation does a good job
> explaining how web developers can use this tag, but we had to do
> some detective work to figure out exactly how to implement it in
> Fennec. For example, Safari's documentation says the content is a
> "comma-delimited list," but existing browsers and web pages use
> any mix of commas, semicolons, and spaces as separators.

This leaves us to believe that although some W3C document says that
both are ok, comma is the more portable choice.

   [1]: https://drafts.csswg.org/css-device-adapt/#viewport-meta
   [2]: https://developer.mozilla.org/en-US/docs/Web/HTML/Viewport_meta_tag

xep.xsl

@@ -191,7 +191,7 @@ content: "XEP-<xsl:value-of select='/xep/header/number'/>";
         <!-- making things mobile-friendly... -->
         <meta>
           <xsl:attribute name='name'><xsl:text>viewport</xsl:text></xsl:attribute>
-          <xsl:attribute name='content'>width=device-width; initial-scale=1.0; maximum-scale=2.0</xsl:attribute>
+          <xsl:attribute name='content'>width=device-width, initial-scale=1.0, maximum-scale=2.0</xsl:attribute>
         </meta>
         <!-- BEGIN META TAGS FOR DUBLIN CORE -->
         <meta>