Add entry for 5.4.2 on Upgrade doc page.

Author: lesserwhirls

docs/src/site/pages/netcdfJava/Upgrade.md

@@ -30,6 +30,7 @@ As such, we no longer utilize WebStart.
 ## netCDF-Java API Changes (5.4.x)
 
 Point release notes:
+* [5.4.2](https://github.com/Unidata/netcdf-java/releases/tag/v5.4.2){:target="_blank"} (_2021-08-26_)
 * [5.4.1](https://github.com/Unidata/netcdf-java/releases/tag/v5.4.1){:target="_blank"} (_2020-12-17_)
 * `5.4.0` was released but not announced.
   It should not be used.