hello world: reinstall deps before npm run install

Without this pass, the subsequent npm run start would fail with:

```
ERROR in ./index.js
Module not found: Error: Can't resolve 'wasm-game-of-life' in '<basedir>/wasm-game-of-life/www'
 @ ./index.js 1:0-42 3:0-10
 @ ./bootstrap.js
```

Author: muxator

src/game-of-life/hello-world.md

@@ -319,6 +319,11 @@ import * as wasm from "wasm-game-of-life";
 wasm.greet();
 ```
 
+Since we declared a new dependency, we need to install it:
+```text
+npm install
+```
+
 Our Web page is now ready to be served locally!
 
 ## Serving Locally