jekyll 1.0 no longer sets a dev flag when serving

[sethladd]

Here's what jekyll 1.0's config looks like:

{"source"=>".",
 "destination"=>"../../build/static",
 "plugins"=>"_plugins",
 "layouts"=>"_layouts",
 "keep_files"=>[".git", ".svn"],
 "timezone"=>nil,
 "safe"=>false,
 "show_drafts"=>nil,
 "limit_posts"=>nil,
 "lsi"=>false,
 "future"=>true,
 "pygments"=>false,
 "markdown"=>"kramdown",
 "permalink"=>"/news/:year/:month/:day/:title.html",
 "baseurl"=>"/",
 "include"=>[".htaccess"],
 "exclude"=>[],
 "paginate_path"=>"page:num",
 "markdown_ext"=>"markdown,mkd,mkdn,md",
 "textile_ext"=>"textile",
 "port"=>"8080",
 "host"=>"0.0.0.0",
 "excerpt_separator"=>"\n\n",
 "maruku"=>
  {"use_tex"=>false,
   "use_divs"=>false,
   "png_engine"=>"blahtex",
   "png_dir"=>"images/latex",
   "png_url"=>"/images/latex"},
 "rdiscount"=>{"extensions"=>[]},
 "redcarpet"=>{"extensions"=>[]},
 "kramdown"=>
  {"auto_ids"=>true,
   "footnote_nr"=>1,
   "entity_output"=>"as_char",
   "toc_levels"=>"2,3",
   "smart_quotes"=>"lsquo,rsquo,ldquo,rdquo",
   "use_coderay"=>false,
   "coderay"=>
    {"coderay_wrap"=>"div",
     "coderay_line_numbers"=>"inline",
     "coderay_line_number_start"=>1,
     "coderay_tab_width"=>4,
     "coderay_bold_every"=>10,
     "coderay_css"=>"style"}},
 "redcloth"=>{"hard_breaks"=>true},
 "server_port"=>8080,
 "custom"=>
  {"downloads"=>
    {"editor-url-prefix"=>"https://storage.googleapis.com/dart-editor-archive",
     "dartium-url-prefix"=>"https://storage.googleapis.com/dartium-archive",
     "binaries"=>
      [{"os"=>"win32", "name"=>"Windows", "ext"=>"zip", "editor-ext"=>"zip"},
       {"os"=>"macos", "name"=>"Mac", "ext"=>"zip", "editor-ext"=>"zip"},
       {"os"=>"linux",
        "name"=>"Linux",
        "ext"=>"tar.gz",
        "editor-ext"=>"zip"}]}},
 "serving"=>true,
 "trace"=>true,
 "watch"=>true}

This breaks asset bundler, because dev is set by looking for a dev flag in config. Which is no longer there.