update rebar to     2.1.0-pre R14B04 20130309_213845      git       2.1....

Updating rebar to a newer version prevents compilation error for new users first pulling the code. 


$ ./rebar compile
==> cb_admin (pre_compile)
ERROR: pre_compile failed while processing /Users/***/Documents/Development/Erlang/cb_admin: {'EXIT',
    {undef,
        [{rebar_config,get_xconf,
             [{config,
                  "/Users/***/Documents/Development/Erlang/ChicagoBoss-0.8.7/cb_admin",
                  [{deps,
                       [{boss,".*",
                            {git,
                                "git://github.com/evanmiller/ChicagoBoss.git",
                                "HEAD"}}]},
                   {plugin_dir,["priv/rebar"]},
                   {plugins,[boss_plugin]},
                   {eunit_compile_opts,[{src_dirs,["src/test"]}]},
                   local]},
              base_dir,undefined],
             []},
         {boss_plugin,init,3,[{file,"priv/rebar/boss_plugin.erl"},{line,64}]},
         {boss_plugin,pre_compile,2,
             [{file,"priv/rebar/boss_plugin.erl"},{line,108}]},
         {rebar_core,run_modules,4,[]},
         {rebar_core,execute,4,[]},
         {rebar_core,process_dir0,6,[]},
         {rebar_core,process_commands,2,[]},
         {rebar,main,1,[]}]}}