fix: Add space to the valid index characters list (#2316)

shared/i18n/locales/en_US/translation.json

@@ -219,7 +219,6 @@
   "Contents": "Contents",
   "Headings you add to the document will appear here": "Headings you add to the document will appear here",
   "Table of contents": "Table of contents",
-  "Contents": "Contents",
   "By {{ author }}": "By {{ author }}",
   "Are you sure you want to make {{ userName }} an admin? Admins can modify team and billing information.": "Are you sure you want to make {{ userName }} an admin? Admins can modify team and billing information.",
   "Are you sure you want to make {{ userName }} a member?": "Are you sure you want to make {{ userName }} a member?",

shared/utils/indexCharacters.js

@@ -1,4 +1,4 @@
 // @flow
 
 export const validateIndexCharacters = (index: string) =>
-  /^[\x21-\x7E]+$/i.test(index);
+  new RegExp("^[\x20-\x7E]+$").test(index);