docs: update web3js guide scripts (#51)

# Description

- Prepping for zksyncdevs threads, I saw there are misspells on scripts,
not sure if someone was checking the scripts.

---------

Co-authored-by: Sabrina <sf@matterlabs.dev>

content/tutorials/guide-web3js/10.index.md

@@ -32,13 +32,13 @@ and [register the plugin](https://docs.web3js.org/guides/web3_plugin_guide/plugi
 
 ```javascript
 import { Web3 } from "web3";
-import { ZkSyncPlugin } from "web3-plugin-zksync";
+import { ZKsyncPlugin } from "web3-plugin-zksync";
 
-const zkSyncRpcUrl: string = "https://sepolia.era.zksync.dev";
+const zksyncRpcUrl: string = "https://sepolia.era.zksync.dev";
 
-console.log(`📞 Connecting to ZKsync Era [${zkSyncRpcUrl}]`);
-const web3: Web3 = new Web3(zkSyncRpcUrl);
-web3.registerPlugin(new ZkSyncPlugin());
+console.log(`📞 Connecting to ZKsync Era [${zksyncRpcUrl}]`);
+const web3: Web3 = new Web3(zksyncRpcUrl);
+web3.registerPlugin(new ZKsyncPlugin(zksyncRpcUrl));
 ```
 
 ::callout{icon="i-heroicons-exclamation-circle"}
@@ -52,8 +52,13 @@ Use the Web3.js `eth` package to fetch data from the ZKsync [Ethereum JSON-RPC A
 #### Fetch the Latest Block Number
 
 ```javascript
-const blockNumber = await web3.eth.getBlockNumber();
-console.log(`Current block number: ${blockNumber}`);
+
+async function main() {
+  const blockNumber = await web3.eth.getBlockNumber();
+  console.log(`Current block number: ${blockNumber}`);
+}
+
+main().catch(console.error);
 ```
 
 ### ZKsync L2-Specific JSON-RPC API
@@ -65,8 +70,12 @@ from the `zks_` namespace of the [JSON-RPC API](https://docs.zksync.io/build/api
 
 <!-- /*spellchecker: disable*/ -->
 ```javascript
-const mainContract = await web3.zkSync.rpc.getMainContract();
-console.log(`Main contract: ${mainContract}`);
+async function main() {
+  const mainContract = await web3.ZKsync.rpc.getMainContract();
+  console.log(`Main contract: ${mainContract}`);
+} 
+
+main().catch(console.error);
 ```
 <!-- /*spellchecker: enable*/ -->