Fix/release script

[alexanderleegs]

Problem

Previously, we were using $npm_config_update to specify the variable used in the npm release script - however, there was a conflict with the npm_config variables used to configure npm itself, causing this script to fail to work as intended. To fix this, we prefix the argument with a unique prefix, converting it to isomer_update instead of update.

Relevant docs: https://docs.npmjs.com/cli/v7/using-npm/config#environment-variables