Update Dangerfile

Dangerfile

@@ -4,9 +4,16 @@ fail 'Please provide a summary in the Pull Request description' if github.pr_bod
 # Warn about develop branch
 warn("Please target PRs to `develop` branch") if github.branch_for_base != "develop"
 
+# Sometimes it's a README fix, or something like that - which isn't relevant for
+# including in a project's CHANGELOG for example
+declared_trivial = github.pr_title.include? "#trivial"
+
 # Make it more obvious that a PR is a work in progress and shouldn't be merged yet
 warn("PR is classed as Work in Progress") if github.pr_title.include? "[WIP]"
 
+# Warn no CHANGELOG
+warn("No CHANGELOG changes made") if git.lines_of_code > 50 && !git.modified_files.include?("CHANGELOG.md") && !declared_trivial
+
 # Warn when there is a big PR
 warn("Big PR") if git.lines_of_code > 500