Markdown --- highlighting for headings

[jhannwong]

[Short description of problem here]

It seems Markdown headings are not highlighted.

Reproduction Steps:

1. Install theme (ui and syntax)
2. Create Markdown file with headings.
3. See the lack of highlighting for headings.

Expected behavior:

[Describe expected behavior here]

Headings should be highlighted.

Observed behavior:

[Describe observed behavior here]

Headings not highlighted.

Screenshots and GIFs

None deemed necessary.

Atom version: 1.27.1 x60
OS and version: MacOS High Sierra 10.13.4

Installed packages:

[List of installed packages here]

• advanced-open-file@0.16.8
• atom-material-syntax@1.0.8
• atom-material-ui@2.1.3
• atomic-emacs@0.12.1
• emmet@2.4.3
• file-watcher@1.2.6
• language-latex@1.1.1
• language-markdown@0.25.1
• language-nginx@0.8.0
• language-restructuredtext@1.1.2
• latex@0.50.0
• markdown-mindmap@0.4.2
• monokai@0.24.0
• pigments@0.40.2
• rst-preview-pandoc@0.1.12
• scratch@1.2.0
• teletype@0.13.3
• termination@0.6.2
• trailing-spaces@0.4.0