Use a "jsonrpc" field rather than "json-rpc" in the VM service.

runtime/vm/service/service.md

 # Dart VM Service Protocol 1.0 (Draft 1)
 
 > Please post feedback to the [observatory-discuss group][discuss-list]
 
 This document describes _draft 1_ of _version 1.0_ of the Dart VM
 Service Protocol.  This protocol is used to communicate with a running
 Dart Virtual Machine.
 
 To use the Service Protocol, start the VM with the *--observe* flag.
 The VM will start a webserver which services protocol requests via WebSocket.
@@ skipping 90 matching lines @@
 optionally accepts requests without the _jsonprc_ property.
 
 An RPC response is a JSON object (http://json.org/). The response always specifies an
 _id_ property to pair it with the corresponding request. If the RPC
 was successful, the _result_ property provides the result.
 
 Here is an example response for our [getVersion](#getversion) request above:
 
 ```
 {
-  "json-rpc": "2.0",
+  "jsonrpc": "2.0",
   "result": {
     "type": "Version",
     "major": 1,
     "minor": 0
   }
   "id": "1"
 }
 ```
 
 Parameters for RPC requests are always provided as _named_ parameters.
@@ skipping 23 matching lines @@
 When an RPC encounters an error, it is provided in the _error_
 property of the response object. JSON-RPC errors always provide
 _code_, _message_, and _data_ properties.
 
 Here is an example error response for our [streamListen](#streamlisten)
 request above. This error would be generated if we were attempting to
 subscribe to the _GC_ stream multiple times from the same client.
 
 ```
 {
-  "json-rpc": "2.0",
+  "jsonrpc": "2.0",
   "error": {
     "code": 103,
     "message": "Stream already subscribed",
     "data": {
       "details": "The stream 'GC' is already subscribed"
     }
   }
   "id": "2"
 }
 ```
@@ skipping 1821 matching lines @@
 ```
 
 ## Revision History
 
 version | comments
 ------- | --------
 1.0 draft 1 | initial revision
 
 
 [discuss-list]: https://groups.google.com/a/dartlang.org/forum/#!forum/observatory-discuss