Frontend: Error loading hui-markdown-card

[aneisch]

Checklist

• [x] I have updated to the latest available Home Assistant version.
• [x] I have cleared the cache of my browser.
• [x] I have tried a different browser to see if it is related to my browser.

The problem

Markdown card fails to load

Custom element doesn't exist: hui-markdown-card.

Expected behavior

Steps to reproduce

Environment

• Home Assistant release with the issue: 0.107
• Last working Home Assistant release (if known): 0.106.6
• Browser and browser version: Chrome 80.0.3987.132 x64
• Operating system: Docker

Problem-relevant configuration

title: Home
icon: mdi:home-circle
cards:
  - !include .cards/thermostat.yaml

  - type: custom:vertical-stack-in-card
    cards:
      - type: markdown
        content: |
          {%- set seconds = (as_timestamp(now()) - as_timestamp(states.input_datetime.front_door_last.state)) | int %}
          {%- set minutes = (seconds // 60) | int %}
          {%- set hours = (minutes // 60) | int %}
          {%- set days = (hours // 24) | int %}
          {{ states.input_datetime.front_door_last.name | capitalize }}: **{{days}}d {{hours%24}}h {{minutes%60}}m**

          {%- set seconds = (as_timestamp(now()) - as_timestamp(states.input_datetime.back_door_last.state)) | int %}
          {%- set minutes = (seconds // 60) | int %}
          {%- set hours = (minutes // 60) | int %}
          {%- set days = (hours // 24) | int %}
          {{ states.input_datetime.back_door_last.name | capitalize }}: **{{days}}d {{hours%24}}h {{minutes%60}}m**

Javascript errors shown in your browser console/inspector

Additional information

[zsarnett]

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