toJSON fails to marshal objects with nested objects

[hairyhenderson]

This is vaguely related to #134.

toJSON behaves badly:

$ gomplate -i '{{ "foo:\n  bar: baz\n" | yaml | toJSON }}'
2017/05/11 21:46:30 Unable to marshal object map[foo:map[bar:baz]]: json: unsupported type: map[interface {}]interface {}

However, toYAML doesn't:

$ gomplate -i '{{ "foo:\n  bar: baz\n" | yaml | toYAML }}'
foo:
  bar: baz

I think the problem is documented in the docs for json.Marshal

Map values encode as JSON objects. The map's key type must either be a string, an integer type, or implement encoding.TextMarshaler.

Obviously gpkg.in/yaml.v2 doesn't have this problem...

🤔