Change name of Roadmap file to capital letters

It's more tradiotonal to name info files in uppercase
See:
https://softwareengineering.stackexchange.com/a/301708/359643

.travis.yml

@@ -15,7 +15,7 @@ jobs:
     - stage: markdownlint
       script: 
       - npm install -g markdownlint-cli
-      - markdownlint CHANGELOG.md Roadmap.md
+      - markdownlint CHANGELOG.md ROADMAP.md
     - stage: spellcheck
       script: 
       - SPELLCHECK_OUT=$(cat CHANGELOG.md | aspell --lang=en --encoding=utf-8 --personal=./.aspell.en.pws list)