Fixes for examples (#1408)

* Add various fixes for the examples
* Add the workaround for proposals for `impl_version` 94
* TODO: fix `toPromise` issue for queries with RxJS

docs/examples/promise/04_unsubscribe/index.js

@@ -9,7 +9,7 @@ async function main () {
   const api = await ApiPromise.create();
 
   // Subscribe to chain updates and log the current block number on update.
-  const unsubscribe = await api.rpc.chain.subscribeNewHead((header) => {
+  const unsubscribe = await api.rpc.chain.subscribeNewHeads((header) => {
     console.log(`Chain is at block: #${header.number}`);
   });