title: I can run with `iex` in terminal, but it doesn't work in my umbrella project
body: <p>I could went into iex mode with command 'iex', but in my umbrella project, what i got is <code>asdf: No version set for command mix</code>.</p>
  
  <pre><code>➜  ~ iex
  Erlang/OTP 21 [erts-10.3] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [hipe]
  
  Interactive Elixir (1.8.2) - press Ctrl+C to exit (type h() ENTER for help)
  iex(1)&gt; 
  </code></pre>
  
  <p>but in project:</p>
  
  <pre><code>➜  ticket_service git:(get-tickets-count-166053245) iex
  asdf: No version set for command iex
  you might want to add one of the following in your .tool-versions file:
  
  elixir 1.8.2-otp-21
  ➜  ticket_service git:(get-tickets-count-166053245) mix compile
  asdf: No version set for command mix
  you might want to add one of the following in your .tool-versions file:
  
  elixir 1.8.2-otp-21
  </code></pre>
  
  <p>BTW, the project is cloned from my github repo, i can even create an new umbrella project and run mix commend everywhere except in my project. It seems like the <code>asdf</code> config is not went into effect in project.</p>