fix: replace apostrophe with empty string in header slugification (#1618)

* Replace apostrophe with empty string in header

This change is to replicate the github behviour with respect to apostrophe in
headers. When there is an apostrophe in a header, github replaces it with empty string
when creating an anchor link to that header. Docusaurus should follow the same convention.

packages/docusaurus-1.x/lib/core/__tests__/toSlug.test.js

@@ -16,6 +16,8 @@ const toSlug = require('../toSlug');
   ['Someting long ...', 'someting-long-'],
   ['foo_bar', 'foo_bar'],
   ['some _ heading', 'some-_-heading'],
+  ["I'm good", 'im-good'],
+  ['This is awes’ome', 'this-is-awesome'],
 ].forEach(([input, output]) => {
   test(`toSlug('${input}') -> '${output}'`, () => {
     expect(toSlug(input)).toBe(output);

packages/docusaurus-1.x/lib/core/toSlug.js

@@ -45,8 +45,8 @@ module.exports = (string, context = {}) => {
     .replace(new RegExp(`[${accents}]`, 'g'), c =>
       without.charAt(accents.indexOf(c)),
     )
-    // Replace `.`, `(` and `?` with blank string like Github does
-    .replace(/\.|\(|\?/g, '')
+    // Replace `'`, `’`, `.`, `(` and `?` with blank string like GitHub does
+    .replace(/'|’|\.|\(|\?/g, '')
     // Dash special characters except '_' (underscore)
     .replace(exceptAlphanumAndUnderscore, '-')
     // Compress multiple dash