Update high resoultion media query

This commit adds a the dppx variant of min-resolution to add an easier
to use value for the media query. `dppx` is not supported by all
browsers and needs the `dpi` fallblack.
`dppx` is more acurate than `dpi` since dots per inch refers to a
defined size of pixels wher one inch is 96px what so ever and does not
take physical inches into account.
Autoprefixer will include `-webkit-min-device-pixel-ratio` which is
needed for Safari and WebKit devices.

Reference #1474.

CHANGELOG.md

@@ -1,3 +1,6 @@
+* Update high resoultion media query
+  ([#1474](https://github.com/h5bp/html5-boilerplate/issues/1474))
+
 ### 5.1.0 (April 1, 2015)
 
 * Update Normalize.css to `v3.0.3`.

dist/css/main.css

@@ -197,6 +197,7 @@ textarea {
 
 @media print,
        (-webkit-min-device-pixel-ratio: 1.25),
+       (min-resolution: 1.25dppx),
        (min-resolution: 120dpi) {
     /* Style adjustments for high resolution devices */
 }

src/css/main.css

@@ -189,6 +189,7 @@ textarea {
 }
 
 @media print,
+       (min-resolution: 1.25dppx),
        (min-resolution: 120dpi) {
     /* Style adjustments for high resolution devices */
 }