doc: simplify wordings in tracing APIs

doc/api/string_decoder.md

@@ -71,7 +71,7 @@ substitution characters appropriate for the character encoding.
 
 If the `buffer` argument is provided, one final call to `stringDecoder.write()`
 is performed before returning the remaining input.
-After `end` is called, the `stringDecoder` object can be reused for new input.
+After `end()` is called, the `stringDecoder` object can be reused for new input.
 
 ### `stringDecoder.write(buffer)`
 <!-- YAML