Update examples for 0.90 (#1225)

* Update examples for 0.90

* Fix number typo

* Adapth to use timestamp.now (blockPeriod now in all versions)

docs/examples/rx/02_listen_to_blocks/index.js

@@ -13,7 +13,7 @@ async function main () {
         api.rpc.chain.subscribeNewHead()
       ))
     .subscribe((header) => {
-      console.log(`Chain is at block: #${header.blockNumber}`);
+      console.log(`Chain is at block: #${header.number}`);
     });
 }
 

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

@@ -12,7 +12,7 @@ async function main () {
         api.rpc.chain.subscribeNewHead()
       ))
     .subscribe((header) => {
-      console.log(`Chain is at block: #${header.blockNumber}`);
+      console.log(`Chain is at block: #${header.number}`);
     });
 
   // In this example we're calling the Overvables unsubscribe() //