Update to the newest WITs

wit/poll.wit

@@ -1,6 +1,6 @@
 /// A poll API intended to let users wait for I/O events on multiple handles
 /// at once.
-default interface poll {
+interface poll {
  /// A "pollable" handle.
  ///
  /// This is conceptually represents a `stream<_, _>`, or in other words,

wit/world.wit

@@ -1,3 +1,5 @@
-default world example-world {
- import poll: pkg.poll
+package wasi:poll
+
+world example-world {
+ import poll
 }