Rake command only clears the "docs" directory

[kaankabalak]

We execute the following when we run rake clean:

task :clean do
    puts "Cleaning up generated docs"
    sh "rm -rf docs"
    sh "rm -f lib/_sidebar.erb"
end

Because we have hardcoded the "docs" directory here, we currently just clear the "docs" directory when we run the command. Users who have generated their files on other directories re-running the gluegun commands will see their files stacked up. We might want to specify the directory we want to clean with the command or we can just take the current directory where the files are being generated into from the .yml file.