helm chart failed to render spark service account when extra annotations are specified

[ChenYi015]

When extra spark serviceaccount annotations are specified in values.yaml:

serviceAccounts:
  spark:
    annotations: 
      key1: value1
      key2: value2

Helm will failed to render template:

$ helm template spark-operator charts/spark-operator-chart -f values.yaml
Error: YAML parse error on spark-operator/templates/spark-serviceaccount.yaml: error unmarshaling JSON: while decoding JSON: json: cannot unmarshal object into Go struct field .metadata.annotations of type string