Enable update_markdown_toc_test

[cgrindel]

The test failed when applying #159. Output:

FAIL: //tests/markdown_tests/tools_tests:update_markdown_toc_test (see /private/var/tmp/_bazel_chuck/de41cc038adf29b29c7e407666a8b614/execroot/cgrindel_bazel_starlib/bazel-out/darwin-fastbuild/testlogs/tests/markdown_tests/tools_tests/update_markdown_toc_test/test.log)
INFO: From Testing //tests/markdown_tests/tools_tests:update_markdown_toc_test:
==================== Test output for //tests/markdown_tests/tools_tests:update_markdown_toc_test:
With defaults Expected to be equal. expected: # Document Title

## Table of Contents

<!-- MARKDOWN TOC: BEGIN -->
* [Chicken](#chicken)
  * [Smidgen](#smidgen)
<!-- MARKDOWN TOC: END -->

## Chicken

### Smidgen, actual: # Document Title

## Table of Contents

<!-- MARKDOWN TOC: BEGIN -->
<!-- MARKDOWN TOC: END -->

## Chicken

### Smidgen
================================================================================

[cgrindel]

The issue appears to be related to how the HTML is generated in the github-markdown-toc.go utility. The tool uses a regexp to extract the header information from HTML generated by GitHub. The order of the anchor attributes changed.