Downgrade custom-selectors plugin for iOS 10

Author: JayPanoz

package-lock.json

@@ -31,7 +31,7 @@
     "postcss-cli": "^11.0.0",
     "postcss-css-variables": "^0.19.0",
     "postcss-custom-media": "^10.0.4",
-    "postcss-custom-selectors": "^7.1.8",
+    "postcss-custom-selectors": "^6.0.0",
     "postcss-discard-comments": "^6.0.2",
     "postcss-header": "^3.0.3",
     "postcss-import": "^16.1.0",