base-lite/ub/ub.go is not the latest source code

Hello,

we have detected that the source code of [base-lite/ub/ub.go](https://github.com/confluentinc/common-docker/blob/master/base-lite/ub/ub.go) is not the latest.

In https://github.com/confluentinc/kafka-images/pull/403/files#diff-50266ac00cfedb6b06dd955cedffd417603555c2e9da4241147c600c51d8387e there are new template functions mentioned, liike `stringSlice` and `envToProps` that can't be found in the ub.go source code.

However, the docker image contains a binary that does indeed have the functions:

```
# /tmp
➜ docker run --rm --entrypoint cat confluentinc/cp-kafka:latest /usr/bin/ub > official-ub
# /tmp
➜ echo '{{- $test := stringSlice "works" -}}{{$test}}' > test.tmpl
# /tmp
➜ chmod +x official-ub
# /tmp
➜ ./official-ub render-template test.tmpl
[works]
# /tmp
```

We are having a hard time running the latest confluent-kafka images without access to the latest `ub.go` source code. Please publish it.