Automatically add new task item with non-breaking spaces

Use `\s` to match the `[[:space:]]` used in ruby
for rendering the task list

app/assets/javascripts/lib/utils/text_markdown.js

@@ -9,7 +9,7 @@ const LINK_TAG_PATTERN = '[{text}](url)';
 // a bullet point character (*+-) and an optional checkbox ([ ] [x])
 // OR a number with a . after it and an optional checkbox ([ ] [x])
 // followed by one or more whitespace characters
-const LIST_LINE_HEAD_PATTERN = /^(?<indent>\s*)(?<leader>((?<isUl>[*+-])|(?<isOl>\d+\.))( \[([xX ])\])?\s)(?<content>.)?/;
+const LIST_LINE_HEAD_PATTERN = /^(?<indent>\s*)(?<leader>((?<isUl>[*+-])|(?<isOl>\d+\.))( \[([xX\s])\])?\s)(?<content>.)?/;
 
 // detect a horizontal rule that might be mistaken for a list item (not full pattern for an <hr>)
 const HR_PATTERN = /^((\s{0,3}-+\s*-+\s*-+\s*[\s-]*)|(\s{0,3}\*+\s*\*+\s*\*+\s*[\s*]*))$/;

spec/frontend/lib/utils/text_markdown_spec.js

@@ -183,6 +183,7 @@ describe('init markdown', () => {
           ${'- [ ] item'}                | ${'- [ ] item\n- [ ] '}
           ${'- [x] item'}                | ${'- [x] item\n- [ ] '}
           ${'- [X] item'}                | ${'- [X] item\n- [ ] '}
+          ${'- [ ] nbsp (U+00A0)'}       | ${'- [ ] nbsp (U+00A0)\n- [ ] '}
           ${'- item\n  - second'}        | ${'- item\n  - second\n  - '}
           ${'- - -'}                     | ${'- - -'}
           ${'- --'}                      | ${'- --'}