Ruby update needed

[Chiper Aurel]

Bug

I am trying to add fastlane to the docker image.
Installed ruby is not compatible with the latest fastlane: 2.137.0

Build error:

 ERROR:  Error installing fastlane:
        signet requires Ruby version >= 2.4.0.

Steps To Reproduce

FROM reactnativecommunity/react-native-android:latest

RUN echo "Update" && apt-get update -y -q

# Fastlane
RUN echo "gem: --no-document" > ~/.gemrc
RUN gem install fastlane -v 2.137.0

WORKDIR /root

[Jiawen Geng]

It's used system default version ruby 2.3.3. It's need extra step to use the latest like

Feel free to send a PR if have time.

RUN sudo apt-get update && \
    cd /tmp && wget -O ruby-install-0.6.1.tar.gz https://github.com/postmodern/ruby-install/archive/v0.6.1.tar.gz && \
    tar -xzvf ruby-install-0.6.1.tar.gz && \
    cd ruby-install-0.6.1 && \
    sudo make install && \
    ruby-install --cleanup ruby && \
    rm -r /tmp/ruby-install-* && \
    sudo rm -rf /var/lib/apt/lists/*

[Jiawen Geng]

fixed via #66