DEV: implementing danger for travis

Dangerfile

@@ -0,0 +1,29 @@
+require 'json'
+
+if git.lines_of_code > 500
+  warn("This PR seems big, we prefer smaller PR. Please be sure this is needed and can’t be split in smaller commits.")
+end
+
+rubocop_output = `bundle exec rubocop --parallel`
+if !rubocop_output.empty?
+  offenses = JSON.parse(rubocop_output)['files']
+    .select { |f| f['offenses'].any? }
+
+  fail(%{
+    This PR has multiple rubocop offenses:
+
+    #{offenses.join("\n")}
+  })
+end
+
+prettier_output = `prettier --list-different "app/assets/stylesheets/**/*.scss" "app/assets/javascripts/**/*.es6" "test/javascripts/**/*.es6" "plugins/**/*.scss" "plugins/**/*.es6"`
+if !prettier_output.empty?
+  offenses = JSON.parse(prettier_output)['files']
+    .select { |f| f['offenses'].any? }
+
+  fail(%{
+    This PR has multiple prettier offenses:
+
+    #{offenses.join("\n")}
+  })
+end