vm: update measure memory rejection information

If in case context is unable to allocate a promise then
`ERR_CONTEXT_NOT_INITIALIZED` error will be thrown (as promise
rejection) in the vm measureMemory call.

doc/api/vm.md

@@ -1061,7 +1061,8 @@ current V8 isolate, or the main context.
     right away to measure the memory.
     **Default:** `'default'`
 * Returns: {Promise} If the memory is successfully measured the promise will
-  resolve with an object containing information about the memory usage.
+  resolve with an object containing information about the memory usage, else it
+  will be rejected with `ERR_CONTEXT_NOT_INITIALIZED` error.
 
 The format of the object that the returned Promise may resolve with is
 specific to the V8 engine and may change from one version of V8 to the next.