Fixed version tag specifier for zkg install command

[javabrett]

Summary of the contribution

zkg install command wouldn't work for me per the docs:

   7 | >>> RUN zkg install --force seisollc/zeek-kafka --version 1.2.0 --user-var librdkafka_root=/usr

9.663 error: invalid package "seisollc/zeek-kafka": no such commit, branch, or version tag: "1.2.0"

Version string needs to exactly match the tag name, so v1.2.0 for latest release.

#6 0.144 + zkg install --force seisollc/zeek-kafka --version v1.2.0 --user-var librdkafka_root=/usr
#6 87.36 Running unit tests for "zeek/seisollc/zeek-kafka"
#6 87.36 Installing "zeek/seisollc/zeek-kafka"
#6 111.2 Installed "zeek/seisollc/zeek-kafka" (v1.2.0)
#6 111.2 Loaded "zeek/seisollc/zeek-kafka"
#6 111.2 + zeek -N Seiso::Kafka
#6 111.5 Seiso::Kafka - Writes logs to Kafka (dynamic, version 0.3.0)

Hopefully this change doesn't upset bump-version.

Testing

...

Checklist

• [x] Confirm that any associated issues are indicated in the pull request title
• [x] Rebase your PR against the latest commit within the target branch
• [x] Include steps to verify and test the intended change
• [ ] Write or update unit tests and/or integration tests to verify your changes
• [ ] Run shellcheck against any new or updated shell scripts, indicating the reasoning behind any disabled checks
• [ ] Indicate whether or not this is a breaking change
• [ ] Ensure that any new dependencies are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0