Add stylelint rule: selector-class-pattern to allow camelcase.

package.json

@@ -168,7 +168,7 @@
       "value-no-vendor-prefix": null,
       "alpha-value-notation": null,
       "color-function-notation": null,
-      "selector-class-pattern":"^[a-z][a-zA-Z0-9]+$|^[A-Z][a-zA-Z0-9]+$"
+      "selector-class-pattern":"^([a-zA-Z]*)(-[a-zA-Z0-9]+)*$|^([a-z][a-z0-9]*)(-[a-z0-9]+)*$"
     }
   }
 }