Update iOS temporal input types support comment (twbs#20343)

* <input type="datetime"> no longer exists, per whatwg/html#336
* iOS 9.3.2 still doesn't support <input type="week">

[skip sauce]
[skip validator]

Author: cvrebert

less/forms.less

@@ -181,7 +181,7 @@ input[type="search"] {
 // set a pixel line-height that matches the given height of the input, but only
 // for Safari. See https://bugs.webkit.org/show_bug.cgi?id=139848
 //
-// Note that as of 8.3, iOS doesn't support `datetime` or `week`.
+// Note that as of 9.3, iOS doesn't support `week`.
 
 @media screen and (-webkit-min-device-pixel-ratio: 0) {
   input[type="date"],