Disable function-no-unknown/no-global function names

The key rule is the second one, as it's not supported in Ruby Sass.

.stylelintrc.json

@@ -7,6 +7,8 @@
         "ignoreAnnotations": ["default", "global"]
       }
     ],
+    "function-no-unknown": null,
+    "scss/no-global-function-names": null,
     "selector-class-pattern": [
       "^[a-z]([-]?[a-z0-9]+)*(__[a-z0-9]([-]?[a-z0-9]+)*)?(--[a-z0-9]([-]?[a-z0-9]+)*)?$",
       {