Fix config types for boxShadow

`boxShadow` accepts multiple shadows just like `dropShadow` does.

Author: tremby

types/config.d.ts

@@ -207,7 +207,7 @@ export interface ThemeConfig {
   caretColor: ThemeConfig['colors']
   accentColor: ThemeConfig['colors']
   opacity: ResolvableTo<KeyValuePair>
-  boxShadow: ResolvableTo<KeyValuePair>
+  boxShadow: ResolvableTo<KeyValuePair<string, string | string[]>>
   boxShadowColor: ThemeConfig['colors']
   outlineWidth: ResolvableTo<KeyValuePair>
   outlineOffset: ResolvableTo<KeyValuePair>