title: UndefinedFunctionError phoenix elixir new project
body: <p>With a fresh install of Phoenix, I tried to trigger a new project, and when I try to run the server, I'm met with:</p>
  
  <pre><code>Unchecked dependencies for environment dev:
   * gettext (Hex package)
    the dependency is not available, run "mix deps.get"
   * phoenix_live_reload (Hex package)
    the dependency is not available, run "mix deps.get"
   * cowboy (Hex package)
   * List item
  ...
  </code></pre>
  
  <p>but when I run <code>mix deps.get</code> I get:</p>
  
  <pre><code>Running dependency resolution
  ** (UndefinedFunctionError) undefined function Access.Map.get_and_update!/3 (module Access.Map is not available)
      Access.Map.get_and_update!(%Mix.Dep{app: :cowboy, deps: [], extra: [], from: "/Users/victoriawagman/Dropbox/Hemsidor/digitalocean/hello_phoenix/mix.exs", manager: nil, opts: [hex: :cowboy, build: "/Users/victoriawagman/Dropbox/Hemsidor/digitalocean/hello_phoenix/_build/dev/lib/cowboy", dest: "/Users/victoriawagman/Dropbox/Hemsidor/digitalocean/hello_phoenix/deps/cowboy"], requirement: "~&gt; 1.0", scm: Hex.SCM, status: {:unavailable, "/Users/victoriawagman/Dropbox/Hemsidor/digitalocean/hello_phoenix/deps/cowboy"}, top_level: true}, :deps, #Function&lt;13.85268495/1 in Hex.Resolver.attach_dep_and_children/3&gt;)
      (hex) lib/hex/resolver.ex:188: Hex.Resolver.attach_dep_and_children/3
      (hex) lib/hex/resolver.ex:148: Hex.Resolver.get_deps/5
      (hex) lib/hex/resolver.ex:107: Hex.Resolver.activate/6
      (hex) lib/hex/resolver.ex:31: Hex.Resolver.resolve/3
      (hex) lib/hex/remote_converger.ex:31: Hex.RemoteConverger.converge/2
      (mix) lib/mix/dep/converger.ex:92: Mix.Dep.Converger.all/4
      (mix) lib/mix/dep/converger.ex:47: Mix.Dep.Converger.converge/4
  </code></pre>
  
  <p>I'm at loss for what to search for to dig deeper into trying to figure out what I can do to understand what is wrong and fix it. Please assume that I have no clue, I'm learning.</p>
  
  <p>Also, I don't know how to separately re-install just hex, so I'm looking for that now, if it is so that I also have a <a href="https://github.com/phoenixframework/phoenix/issues/1307">corrupt install of hex</a>.</p>