Add markdown format support (#25)

Co-authored-by: Dawid Dziurla <dawidd0811@gmail.com>

node_modules/showdown/.travis.yml

@@ -0,0 +1,26 @@
+language: node_js
+node_js:
+  - "6"
+  - "8"
+  - "10"
+
+before_install:
+  - npm install -g grunt-cli
+
+# travis build  speed up
+sudo: false
+cache:
+  directories:
+    - node_modules
+
+# scripts
+script: grunt test
+
+# hooks
+notifications:
+  webhooks:
+    urls:
+      - 'https://webhooks.gitter.im/e/e369617839852624aa69'
+    on_success: change  # options: [always|never|change] default: always
+    on_failure: always  # options: [always|never|change] default: always
+    on_start: false     # default: false