title: rvm upgrade error with 'command gem pristine --extensions debugger --version 1.6.0 failed'
body: <p>I'm getting this error when upgrading ruby with rvm:</p>
  
  <pre><code>Error running '__rvm_with ruby-2.1.5 gemset_pristine',
  showing last 15 lines of /Users/snowcrash/.rvm/log/1419348453/gemset.pristine-ruby-2.1.5.log
  + gem pristine --extensions yard --version 0.8.6.2
  + read _gem _version _platforms
  + ((  1 &gt; 0  ))
  + rvm_error '\n'\''command gem pristine --extensions debugger --version 1.6.0'\'' failed, you need to fix this gems manually.'
  + rvm_pretty_print stderr
  + case "${rvm_pretty_print_flag:=auto}" in
  + case "${TERM:-dumb}" in
  + case "$1" in
  + [[ -t 2 ]]
  + return 1
  + printf %b '\n'\''command gem pristine --extensions debugger --version 1.6.0'\'' failed, you need to fix this gems manually.\n'
  
  'command gem pristine --extensions debugger --version 1.6.0' failed, you need to fix this gems manually.
  + return 1
  </code></pre>
  
  <p>Any suggestions on how to fix?</p>