title: Rails cannot install gem 'unf'
body: <p>Whenever I try: <code>$ gem install unf</code>,  I get this error :</p>
  
  <pre><code>ERROR:  While executing gem ... (NoMethodError)
      undefined method `spec' for nil:NilClass
  </code></pre>
  
  <p>I even tried adding these libraries</p>
  
  <pre><code>sudo apt-get install build-essential openssl libreadline6 libreadline6-dev curl git-core     zlib1g zlib1g-dev libssl-dev libyaml-dev libsqlite3-0 libsqlite3-dev sqlite3 libxml2-dev libxslt-dev autoconf libc6-dev ncurses-dev automake libtool bison
  </code></pre>
  
  <p>but no cigar, any idea what I should do ?</p>