Fix gem installation

Author: ferrarimarco

Dockerfile

@@ -1,18 +1,24 @@
-FROM ruby:2.6.4-alpine3.9
+FROM ruby:2.7.3-alpine3.13
 
 LABEL maintainer="[email protected]"
 
 SHELL ["/bin/ash", "-eo", "pipefail", "-c"]
 
 RUN apk add --no-cache \
-  git=2.20.4-r0
+  git=2.30.2-r0
 
 WORKDIR /
 COPY Gemfile Gemfile
-RUN gem install bundler --version 2.2.15 \
-  && bundle install --system \
+RUN apk add --no-cache \
+  --virtual .gem-installdeps \
+  build-base=0.5-r2 \
+  && gem install bundler --version 2.2.15 \
+  && bundle config set --local system 'true' \
+  && bundle install \
   && gem uninstall bundler \
-  && rm Gemfile
+  && rm Gemfile Gemfile.lock \
+  && rm -rf $GEM_HOME/cache \
+  && apk del .gem-installdeps
 
 ENV SRC_PATH /usr/local/src/your-app
 RUN mkdir -p "${SRC_PATH}"