Simplify Dockerfile commands and update RubyGems

Author: tsusdere

Dockerfile

@@ -1,14 +1,14 @@
 ARG RUBY_VERSION
 FROM ruby:$RUBY_VERSION-slim
 RUN set -ex \
-    # Update RubyGems system if Ruby version is 3.1 or higher
-    && if ruby -e 'exit(RUBY_VERSION.to_f >= 3.1)'; then \
-         gem update --system; \
-       fi \
-    && apt-get update -y \
-    && apt-get upgrade -y \
-    && apt-get install -y build-essential git libcurl4-openssl-dev \
-    && apt-get clean
+  && gem update --system --silent --quiet \
+  && apt-get update -y \
+  && apt-get upgrade -y \
+  && apt-get install -y \
+    build-essential \
+    git \
+    libcurl4-openssl-dev \
+  && apt-get clean
 WORKDIR /app/github-pages-health-check
 COPY Gemfile .
 COPY github-pages-health-check.gemspec .