fix: bad request body simple in propertykey.md

[wangyao2016]

An error will be reported according to the original document, like:

Unrecognized field "property_key" (class com.baidu.hugegraph.api.schema.PropertyKeyAPI$JsonPropertyKey), not marked as ignorable (9 known properties: "check_exist", "properties", "aggregate_type", "id", "cardinality", "data_type", "name", "user_data", "write_type"])
 at [Source: (org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream); line: 2, column: 23] (through reference chain: com.baidu.hugegraph.api.schema.PropertyKeyAPI$JsonPropertyKey["property_key"])

[imbajin]

thanks for your contribution, could u submit it based on website branch? current master will not be used soon

u could refer the README in website & correct it in both EN & CN files

[wangyao2016]

website

Got it, please see this pr 135, thanks for help.