fix: fix jq command when working with an existing Docker config.json file

[ahamilton55]

Checklist

• All new jobs, commands, executors, parameters have descriptions (not needed)
• Examples have been added for any significant new features (not needed)
• README has been updated, if necessary (not needed)

Motivation, issues

Fixes #333

The change is needed to update the ${HOME}/.docker/config.json file to with multiple ECR entries. The jq command currently fails when attempting to add a second ECR entry.

Description

Removes double quotes around the $jq_flag so that it is properly handled when it is empty. With the double quotes, the jq command is interpreting the empty string as a parameter and then failing to find the config file because of how it is parsing the flags.

I also fix the indentation of the jq command so that the staring matches the level of the if statement above it and indent the additional parts of the jq command a couple extra spaces.