The output of `kubectl version` has changed with newer kubectl version
from
```
{
"serverVersion": ...,
"clientVersion": ...
}
```
to
```
{
"serverVersion": ...,
"clientVersion": ...,
"kustomizeVersion": ...
}
```
So the `kustomizeVersion` field is new which causes the JSON
unmarshaling to fail.
We now just unmarshal it to `map[string]interface{}` and peel the
server git version out of that map manually w/o unmarshalling the JSON
into a custom type.
Signed-off-by: Max Jonas Werner <mail@makk.es>
9af6175302