Make build use spawnAndCheck (#467)

I think this is the reason I didn't notice it fail.
The build was using just spawn and so when rollup failed it
didn't pass the exit status back out to the action so
the action though the build succeeded.

build/lib/spawn.js

@@ -0,0 +1,16 @@
+import { spawn } from 'child_process';
+
+const spawns = new Set();
+
+export function spawnAndCheck(cmd, args, options) {
+  const s = spawn(cmd, args, options);
+  spawns.add(s);
+  s.on('close', (code) => {
+    spawns.delete(s);
+    if (code !== 0) {
+      console.error(cmd, 'exited with code:', code);
+      [...spawns].forEach((s) => s.kill());
+      process.exit(code);
+    }
+  });
+}

build/tools/build.js

@@ -1,14 +1,14 @@
-import { spawn } from 'child_process';
 import { mkdirSync } from 'fs';
+import { spawnAndCheck } from '../lib/spawn.js';
 
 mkdirSync('out', { recursive: true });
 
-spawn('node', ['build/tools/copy.js'], {
+spawnAndCheck('node', ['build/tools/copy.js'], {
   shell: true,
   stdio: 'inherit',
 });
 
-spawn('./node_modules/.bin/rollup', ['-c'], {
+spawnAndCheck('./node_modules/.bin/rollup', ['-c'], {
   shell: true,
   stdio: 'inherit',
 });

build/tools/serve.js

@@ -1,23 +1,8 @@
-import { spawn } from 'child_process';
 import { mkdirSync } from 'fs';
+import { spawnAndCheck } from '../lib/spawn.js';
 
 mkdirSync('out', { recursive: true });
 
-const spawns = new Set();
-
-function spawnAndCheck(cmd, args, options) {
-  const s = spawn(cmd, args, options);
-  spawns.add(s);
-  s.on('close', (code) => {
-    spawns.delete(s);
-    if (code !== 0) {
-      console.error(cmd, 'exited with code:', code);
-      [...spawns].forEach((s) => s.kill());
-      process.exit(code);
-    }
-  });
-}
-
 spawnAndCheck('npm', ['run', 'watch'], {
   shell: true,
   stdio: 'inherit',