fix(core): normalize input for poll option

This change normalizes input for the poll option to either a boolean or number to meet the specs required by Webpack config

fixes facebook#8306

packages/docusaurus/bin/docusaurus.mjs

@@ -22,6 +22,7 @@ import {
   writeTranslations,
   writeHeadingIds,
 } from '../lib/index.js';
+import {normalizePollValue} from './utils.mjs';
 import beforeCli from './beforeCli.mjs';
 
 await beforeCli();
@@ -122,6 +123,7 @@ cli
   .option(
     '--poll [interval]',
     'use polling rather than watching for reload (default: false). Can specify a poll interval in milliseconds',
+    normalizePollValue,
   )
   .option(
     '--no-minify',

packages/docusaurus/bin/utils.mjs

@@ -0,0 +1,24 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+/**
+ *
+ * @param {string} value
+ * @returns {boolean|number}
+ */
+export function normalizePollValue(value) {
+  if (value === undefined || value === '') {
+    return false;
+  }
+
+  const parsedIntValue = Number.parseInt(value, 10);
+  if (!Number.isNaN(parsedIntValue)) {
+    return parsedIntValue;
+  }
+
+  return value === 'true';
+}