Small release notes fixup

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>
Fix JSON string length calculations

A JSON String length is the number of its Unicode code points; unfortunately,
String's .length() counts the number of `char`s, that is the number of UTF-16
code units.

But for Unicode code points outside the BMP, UTF-16 requires two code units, and
String two `char`s as well.

Change the length calculation by calling .codePointCount() instead.

Fixes: #92

Signed-off-by: Francis Galiegue <fgaliegue@gmail.com>