Update pinned wasm-bindgen dependency (#6861)

* Update dependency.

* Update readme docs

* update python webserver command

substrate/bin/node/cli/browser-demo/README.md

@@ -1,6 +1,10 @@
 # How to run this demo
 
 ```sh
-cargo install wasm-bindgen-cli		# If necessary
+# If necessary, install wasm-bindgen
+# The version must match that used when building the browser demo.
+cargo install --version 0.2.67 wasm-bindgen-cli
+
+# Run the build script
 ./build.sh
 ```

substrate/bin/node/cli/browser-demo/build.sh

@@ -1,4 +1,4 @@
 #!/usr/bin/env sh
 cargo +nightly build --release -p node-cli --target wasm32-unknown-unknown --no-default-features --features browser -Z features=itarget
 wasm-bindgen ../../../../target/wasm32-unknown-unknown/release/node_cli.wasm --out-dir pkg --target web
-python -m http.server 8000
+python -m SimpleHTTPServer 8000