Grammar is pulled as YAML from slim-template/ruby-slim.tmbundle and converted to CSON, additional changes might be done to the resulting grammars/ruby slim.cson file.
npm installwget https://raw.githubusercontent.com/slim-template/ruby-slim.tmbundle/master/Syntaxes/Ruby%20Slim.YAML-tmLanguagenode_modules/.bin/yaml2json "Ruby Slim.YAML-tmLanguage" -p | node_modules/.bin/json2cson --2spaces > "grammars/ruby slim.cson"
Optionally, make changes to grammars/ruby slim.cson. Preview the results by rebuilding/linking the package and previewing demo.slim.
apm rebuild && apm link && atom .
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.