rbnev install 2.1.2 - Wrong owner for .rbenv/versions/2.1.2/lib/ruby/gems/2.1.0 directory

dir_listing.log

$ docker run -t -i ffd83eded638 bash
To run a command as administrator (user "root"), use "sudo <command>".
See "man sudo_root" for details.

ubuntu@819cb540484b:~$ ll /home/ubuntu/.rbenv/versions/2.1.2/lib/ruby/gems
total 12
drwxr-xr-x 3 root root 4096 Jun 26 16:49 ./
drwxr-xr-x 6 root root 4096 Jun 26 16:49 ../
drwxr-xr-x 8 root root 4096 Jun 26 16:49 2.1.0/
ubuntu@819cb540484b:~$ ll .rbenv/versions/
total 16
drwxr-xr-x  4 ubuntu ubuntu 4096 Jun 26 16:44 ./
drwxr-xr-x 14 ubuntu ubuntu 4096 Jun 26 16:52 ../
drwxr-xr-x  6 ubuntu ubuntu 4096 Dec  4  2013 2.0.0-p353/
drwxr-xr-x  6 root   root   4096 Jun 26 16:49 2.1.2/

docker_build.log

docker build .
Uploading context 3.584 kB
Uploading context
Step 0 : FROM bradrydzewski/base
 ---> 00fb4af118c1
Step 1 : WORKDIR /home/ubuntu
 ---> Using cache
 ---> 91a2d1b17810
Step 2 : USER ubuntu
 ---> Using cache
 ---> ccb0fc858bee
Step 3 : ADD rbenv.sh /etc/drone.d/
 ---> Using cache
 ---> b4863ac9f15d
Step 4 : RUN cd /home/ubuntu/.rbenv/plugins/ruby-build &&    git pull
 ---> Using cache
 ---> 7c84559ad908
Step 5 : RUN export PATH="/home/ubuntu/.rbenv/bin:$PATH" &&    rbenv install 2.1.2 &&    rbenv global 2.1.2 &&    rbenv rehash
 ---> Running in 1c05c7b3cd79
Downloading ruby-2.1.2.tar.gz...
-> http://dqw8nmjcqpjn7.cloudfront.net/f22a6447811a81f3c808d1c2a5ce3b5f5f0955c68c9a749182feb425589e6635
Installing ruby-2.1.2...
Installed ruby-2.1.2 to /home/ubuntu/.rbenv/versions/2.1.2

 ---> ffd83eded638
Step 6 : RUN export PATH="/home/ubuntu/.rbenv/bin:$PATH" &&    eval "$(rbenv init -)" &&    gem install bundler &&    rbenv rehash
 ---> Running in a4db55bf6b12
ERROR:  While executing gem ... (Gem::FilePermissionError)
    You don't have write permissions for the /home/ubuntu/.rbenv/versions/2.1.2/lib/ruby/gems/2.1.0 directory.
2014/06/26 22:50:00 The command [/bin/sh -c export PATH="/home/ubuntu/.rbenv/bin:$PATH" &&    eval "$(rbenv init -)" &&    gem install bundler &&    rbenv rehash] returned a non-zero code: 1

Dockerfile

FROM bradrydzewski/base

WORKDIR /home/ubuntu
USER ubuntu
ADD rbenv.sh /etc/drone.d/

RUN cd /home/ubuntu/.rbenv/plugins/ruby-build && \
    git pull

RUN export PATH="/home/ubuntu/.rbenv/bin:$PATH" && \
    rbenv install 2.1.2 && \
    rbenv global 2.1.2 && \
    rbenv rehash

RUN export PATH="/home/ubuntu/.rbenv/bin:$PATH" && \
    eval "$(rbenv init -)" && \
    gem install bundler && \
    rbenv rehash