Add the ruby implementation of hello-world

[refs #64aaa3a626be]

Author: jfahrer

developing/hello-world/Dockerfile

@@ -0,0 +1,7 @@
+FROM ruby:2.4.3-alpine
+
+WORKDIR /app
+
+COPY app.rb .
+
+CMD ruby app.rb

developing/hello-world/app.rb

@@ -0,0 +1 @@
+puts 'Hello World!'