Fix docs updates on prereleases

(cherry picked from commit f0316a4cefc5526b9e052e77b5c29b6a715d4f98)

scripts/update-docs-branch.js

@@ -21,6 +21,13 @@ if (!match) {
   process.exit(1);
 }
 
+const pkgVersion = require('../package.json').version;
+
+if (pkgVersion.includes('-') && !pkgVersion.includes('.0.0-')) {
+  console.error('Refusing to update docs: non-major prerelease detected');
+  process.exit(0);
+}
+
 const current = match.groups;
 const docsBranch = `docs-v${current.major}.x`;