update ruby and bundle version (#2503)

* update ruby and bundle version

* Update docs/serving/samples/hello-world/helloworld-ruby/Gemfile.lock

Co-authored-by: Matt Moore <[email protected]>

* update README

Co-authored-by: Matt Moore <[email protected]>

Author: xiangshen-dk

docs/serving/samples/hello-world/helloworld-ruby/Dockerfile

@@ -1,12 +1,12 @@
 # Use the official lightweight Ruby image.
 # https://hub.docker.com/_/ruby
-FROM ruby:2.5-slim
+FROM ruby:2.6-slim
 
 # Install production dependencies.
 WORKDIR /usr/src/app
 COPY Gemfile Gemfile.lock ./
 ENV BUNDLE_FROZEN=true
-RUN bundle install
+RUN gem install bundler && bundle install
 
 # Copy local code to the container image.
 COPY . ./

docs/serving/samples/hello-world/helloworld-ruby/Gemfile.lock

@@ -1,16 +1,18 @@
 GEM
   remote: https://rubygems.org/
   specs:
-    mustermann (1.0.2)
-    rack (2.0.8)
-    rack-protection (2.0.3)
+    mustermann (1.1.1)
+      ruby2_keywords (~> 0.0.1)
+    rack (2.2.2)
+    rack-protection (2.0.8.1)
       rack
-    sinatra (2.0.3)
+    ruby2_keywords (0.0.2)
+    sinatra (2.0.8.1)
       mustermann (~> 1.0)
       rack (~> 2.0)
-      rack-protection (= 2.0.3)
+      rack-protection (= 2.0.8.1)
       tilt (~> 2.0)
-    tilt (2.0.8)
+    tilt (2.0.10)
 
 PLATFORMS
   ruby
@@ -20,4 +22,4 @@ DEPENDENCIES
   sinatra
 
 BUNDLED WITH
-   1.17.1
+   2.1.4

docs/serving/samples/hello-world/helloworld-ruby/README.md

@@ -48,13 +48,13 @@ cd knative-docs/docs/serving/samples/hello-world/helloworld-ruby
    ```docker
    # Use the official lightweight Ruby image.
    # https://hub.docker.com/_/ruby
-   FROM ruby:2.5-slim
+   FROM ruby:2.6-slim
 
    # Install production dependencies.
    WORKDIR /usr/src/app
    COPY Gemfile Gemfile.lock ./
    ENV BUNDLE_FROZEN=true
-   RUN bundle install
+   RUN gem install bundler && bundle install
 
    # Copy local code to the container image.
    COPY . ./