Failed creating providers when elixir_opts is not defined

[kalouantonis]

This is not a duplicate of #15, in my case I did not define elixir_opts and got the same exception.

➜  DEBUG=1 rebar3 compile
===> Load global config file /Users/slacker/.config/rebar3/rebar.config
===> Not adding provider default auto from module rebar3_auto because it already exists from module rebar3_auto
===> error: {badmatch,error} [{rebar_state,get,2,
                                      [{file,
                                        "/home/tristan/Devel/rebar3/_build/default/lib/rebar/src/rebar_state.erl"},
                                       {line,150}]},
                                     {rebar3_elixir_compile_util,get_details,
                                      1,
                                      [{file,
                                        "/Users/slacker/Programming/irresponsible/sellery/_build/default/plugins/rebar3_elixir_compile/src/rebar3_elixir_compile_util.erl"},
                                       {line,56}]},
                                     {rebar3_elixir_compile,init,1,
                                      [{file,
                                        "/Users/slacker/Programming/irresponsible/sellery/_build/default/plugins/rebar3_elixir_compile/src/rebar3_elixir_compile.erl"},
                                       {line,8}]},
                                     {rebar_state,
                                      '-create_logic_providers/2-fun-0-',2,
                                      [{file,
                                        "/home/tristan/Devel/rebar3/_build/default/lib/rebar/src/rebar_state.erl"},
                                       {line,409}]},
                                     {lists,foldl,3,
                                      [{file,"lists.erl"},{line,1263}]},
                                     {rebar_state,create_logic_providers,2,
                                      [{file,
                                        "/home/tristan/Devel/rebar3/_build/default/lib/rebar/src/rebar_state.erl"},
                                       {line,408}]},
                                     {rebar_plugins,
                                      '-handle_plugins/4-fun-0-',4,
                                      [{file,
                                        "/home/tristan/Devel/rebar3/_build/default/lib/rebar/src/rebar_plugins.erl"},
                                       {line,84}]},
                                     {lists,foldl,3,
                                      [{file,"lists.erl"},{line,1263}]}]
===> Failed creating providers. Run with DEBUG=1 for stacktrace or consult rebar3.crashdump.
➜  

I'll be submitting a PR to fix this.

[benoitc]

just merged it thanks!