Check if cargo already from nighlty in wasm build scripts (#724)

substrate/node/runtime/wasm/build.sh

@@ -1,7 +1,12 @@
 #!/usr/bin/env bash
 set -e
 
-cargo +nightly build --target=wasm32-unknown-unknown --release
+if cargo --version | grep -q "nightly"; then
+	CARGO_CMD="cargo"
+else
+	CARGO_CMD="cargo +nightly"
+fi
+$CARGO_CMD build --target=wasm32-unknown-unknown --release
 for i in node_runtime
 do
 	wasm-gc target/wasm32-unknown-unknown/release/$i.wasm target/wasm32-unknown-unknown/release/$i.compact.wasm