Update rebar.config

Fixes build error with lager version mismatch (I think).

It now builds and runs according to turorial 1 if I run the command twice (the first time it gets deps but doesn't compile anything).


```
make rel
/Users/nruth/dev/syncfree/crdtdb/rebar get-deps
/Users/nruth/dev/syncfree/crdtdb/rebar compile
==> Entering directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/lager'
==> Entering directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/lager'
==> Entering directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/goldrush'
==> Entering directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/goldrush'
==> goldrush (compile)
==> goldrush (get-deps)
==> Leaving directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/goldrush'
==> lager (get-deps)
==> Leaving directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/lager'
==> Entering directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/riak_core'
==> riak_core (get-deps)
ERROR: Dependency dir /Volumes/case-sensitive/dev/syncfree/crdtdb/deps/lager failed application validation with reason:
{version_mismatch,{"/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/lager/src/lager.app.src",
                   {expected,"2.0.3"},
                   {has,"2.0.0"}}}.
make: *** [deps] Error 1
make: *** Waiting for unfinished jobs....
Compiled src/glc.erl
Compiled src/glc_lib.erl
Compiled src/glc_code.erl
Compiled src/gr_context.erl
Compiled src/gre.erl
Compiled src/glc_ops.erl
==> Leaving directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/goldrush'
==> lager (compile)
Compiled src/lager_util.erl
Compiled src/lager_transform.erl
Compiled src/lager_app.erl
Compiled src/lager_backend_throttle.erl
Compiled src/lager.erl
Compiled src/lager_config.erl
Compiled src/lager_console_backend.erl
Compiled src/error_logger_lager_h.erl
Compiled src/lager_crash_log.erl
Compiled src/lager_default_formatter.erl
Compiled src/lager_handler_watcher.erl
Compiled src/lager_handler_watcher_sup.erl
Compiled src/lager_msg.erl
Compiled src/lager_file_backend.erl
Compiled src/lager_format.erl
Compiled src/lager_sup.erl
Compiled src/lager_stdlib.erl
Compiled src/lager_trunc_io.erl
==> Leaving directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/lager'
==> Entering directory `/Volumes/case-sensitive/dev/syncfree/crdtdb/deps/riak_core'
==> riak_core (compile)
Dependency not available: lager-2.0.3 ({git,
                                        "git://github.com/basho/lager.git",
                                        {tag,"2.0.3"}})
Dependency not available: poolboy-.* ({git,
                                       "git://github.com/basho/poolboy.git",
                                       {tag,"0.8.1p2"}})
Dependency not available: basho_stats-.* ({git,
                                           "git://github.com/basho/basho_stats.git",
                                           {tag,"1.0.3"}})
Dependency not available: riak_sysmon-.* ({git,
                                           "git://github.com/basho/riak_sysmon.git",
                                           {branch,"develop"}})
Dependency not available: folsom-0.7.4p4 ({git,
                                           "git://github.com/basho/folsom.git",
                                           {tag,"0.7.4p4"}})
Dependency not available: riak_ensemble-.* ({git,
                                             "git://github.com/basho/riak_ensemble",
                                             {branch,"develop"}})
Dependency not available: pbkdf2-.* ({git,
                                      "git://github.com/basho/erlang-pbkdf2.git",
                                      {tag,"2.0.0"}})
Dependency not available: eleveldb-.* ({git,
                                        "git://github.com/basho/eleveldb.git",
                                        {branch,"develop"}})
make: *** [compile] Error 1
```