Fix wrong type of downloaddetails in templateresponse

[davidjumani]

Before :

ts := cloudstack.NewTemplateService(cs)
p := ts.NewListTemplatesParams("all")
r, err := ts.ListTemplates(p)


json: cannot unmarshal array into Go struct field ListTemplatesResponse.template of type string

After :

&{4 [0xc0000b6a00 0xc0000b6c80 0xc0000b6f00 0xc0000b7180]}

Hide the whitespaces in the diff to save yourself