Prefer direct Hash access

Since we've already confirmed the key exists with we can safely use
`@styles[style_name]` instead of `@styles.fetch(style_name)` for direct
hash access.

Author: koppen

app/components/flowbite/styles.rb

@@ -19,7 +19,7 @@ def add_style(style_name, states_hash)
     end
 
     def fetch(style_name)
-      return @styles.fetch(style_name) if @styles.key?(style_name)
+      return @styles[style_name] if @styles.key?(style_name)
 
       raise \
         StyleNotFoundError,