Update SUMMARY.md

Author: simonsan

SUMMARY.md

@@ -1,7 +1,7 @@
 # Summary
 
 - [Introduction](./intro.md)
-  - [Translation](./translations.md)
+  - [Translations](./translations.md)
 - [Idioms](./idioms/index.md)
   - [Use borrowed types for arguments](./idioms/coercion-arguments.md)
   - [Concatenating Strings with `format!`](./idioms/concat-format.md)