chore(library): add gettext (#82)
chore(library): add gettext (#82)

because `envsubst` is very useful in certain scenarios.

e.g:

```yaml
# helm/values.yaml file
configmap:
    MYSQL_USERNAME: ${MYSQL_USERNAME}
```

```shell
export MYSQL_USERNAME=root

export VALUES=`envsubst < helm/values.yaml`
echo $VALUES > helm/values.yaml

cat helm/values.yaml
# => configmap:
# =>     MYSQL_USERNAME: root
```
dtzar/helm-kubectl