Swap out the complicated canary stuff for serial execution

Fixes https://github.com/vector-im/riot-web/issues/7386

scripts/npm-sub.js

@@ -0,0 +1,21 @@
+const path = require('path');
+const child_process = require('child_process');
+
+const moduleName = process.argv[2];
+if (!moduleName) {
+    console.error("Expected module name");
+    process.exit(1);
+}
+
+const argString = process.argv.length > 3 ? process.argv.slice(3).join(" ") : "";
+if (!argString) {
+    console.error("Expected an npm argument string to use");
+    process.exit(1);
+}
+
+const modulePath = path.dirname(require.resolve(`${moduleName}/package.json`));
+
+child_process.execSync("npm " + argString, {
+    env: process.env,
+    cwd: modulePath,
+});