docs: update ping API docs

Author: Alan Shaw

SPEC/MISCELLANEOUS.md

@@ -111,9 +111,9 @@ Where:
 
 | Type | Description |
 | -------- | -------- |
-| `Promise<Array>` | An array of ping response objects |
+| `AsyncIterable<Object>` | An async iterable that yields ping response objects |
 
-an array of objects is returned, each of the form:
+Each yielded object is of the form:
 
 ```js
 {
@@ -128,14 +128,13 @@ Note that not all ping response objects are "pongs". A "pong" message can be ide
 **Example:**
 
 ```JavaScript
-const responses = await ipfs.ping('Qmhash')
-responses.forEach((res) => {
+for await (const res of ipfs.ping('Qmhash')) {
   if (res.time) {
     console.log(`Pong received: time=${res.time} ms`)
   } else {
     console.log(res.text)
   }
-})
+}
 ```
 
 A great source of [examples](https://github.com/ipfs/interface-ipfs-core/tree/master/src/ping) can be found in the tests for this API.