Prevent users from zooming in IE Mobile

Fixes #7499

According to https://msdn.microsoft.com/en-us/library/dn629259(v=vs.85).aspx,
“the minimum-scale, maximum-scale, and initial-scale properties are currently
unsupported for Internet Explorer for Windows Phone“.

For further information on the viewport properties see
https://drafts.csswg.org/css-device-adapt/#viewport-meta

closes #7589

Changelog.md

@@ -12,6 +12,7 @@
 * Fix displaying polls with long answers [#7579](https://github.com/diaspora/diaspora/pull/7579)
 * Fix S3 support [#7566](https://github.com/diaspora/diaspora/pull/7566)
 * Fix mixed username and timestamp with LTR/RTL scripts [#7575](https://github.com/diaspora/diaspora/pull/7575)
+* Prevent users from zooming in IE Mobile [#7589](https://github.com/diaspora/diaspora/pull/7589)
 
 ## Features
 * Ask for confirmation when leaving a submittable comment field [#7530](https://github.com/diaspora/diaspora/pull/7530)

app/views/layouts/application.mobile.haml

@@ -12,7 +12,7 @@
     = render "head"
     = include_color_theme "mobile"
 
-    %meta{name: "viewport", content: "width=device-width, minimum-scale=1 maximum-scale=1"}/
+    %meta{name: "viewport", content: "width=device-width, minimum-scale=1, maximum-scale=1, user-scalable=no"}/
     %meta{name: "HandheldFriendly", content: "True"}/
     %meta{name: "MobileOptimized", content: "320"}/
     %meta{"http-equiv" => "cleartype", :content => "on"}/