check that latest version appears in changelog (#9071)

This prevents an update to package.json from being merged without
including a corresponding change to the changelog.

This will prevent me from forgetting to remove `-beta` from the
changelog when doing a final release.

test/unit/changelog.js

@@ -0,0 +1,17 @@
+import {test} from '../util/test';
+import fs from 'fs';
+import path from 'path';
+import {version} from '../../package.json';
+
+test('changelog', (t) => {
+    const changelog = fs.readFileSync(path.join(__dirname, '../../CHANGELOG.md'), 'utf8');
+    t.test('latest version is in changelog', (t) => {
+        if (version.indexOf('-dev') <= 0) {
+            const versionString = `## ${version}\n`;
+            t.ok(changelog.indexOf(versionString) >= 0);
+        }
+        t.end();
+    });
+
+    t.end();
+});