yarn install before yarn build

.gitignore

@@ -1,5 +1,4 @@
 /target
-/Cargo.lock
 dist
 node_modules
 out

Makefile

@@ -4,6 +4,7 @@ pkg/matzo_web_bg.wasm: src/lib.rs Cargo.toml Cargo.lock
 	wasm-pack build --target web
 
 dist/main.js: js/*.js package.json pkg/matzo_web_bg.wasm
+	yarn install
 	yarn build
 
 out/index.html: index.html build.py examples/*.matzo