Index: node_modules/autoprefixer/lib/hacks/image-set.js
===================================================================
--- node_modules/autoprefixer/lib/hacks/image-set.js	(revision 2058e5c694bb6097866a5fe6503c519e8f74970f)
+++ node_modules/autoprefixer/lib/hacks/image-set.js	(revision 2058e5c694bb6097866a5fe6503c519e8f74970f)
@@ -0,0 +1,18 @@
+let Value = require('../value')
+
+class ImageSet extends Value {
+  /**
+   * Use non-standard name for WebKit and Firefox
+   */
+  replace(string, prefix) {
+    let fixed = super.replace(string, prefix)
+    if (prefix === '-webkit-') {
+      fixed = fixed.replace(/("[^"]+"|'[^']+')(\s+\d+\w)/gi, 'url($1)$2')
+    }
+    return fixed
+  }
+}
+
+ImageSet.names = ['image-set']
+
+module.exports = ImageSet