Bump Ruby development execution environment (#2994)

Updated Ruby execution environment in development to remove
Docker V1 support requirement.

Relates to #2993

Author: arkirchner

db/seeds/files/exercise_spec.rb

@@ -2,10 +2,10 @@
 
 require './exercise'
 
-describe '#write_to_file' do
+describe '#copy_file' do
   before(:each) do
     @file_content = File.new(SOURCE_FILENAME, 'r').read
-    write_to_file
+    copy_file
   end
 
   it 'preserves the source file' do

spec/factories/execution_environment.rb

@@ -109,10 +109,10 @@
     created_by_teacher
     default_memory_limit
     default_cpu_limit
-    docker_image { 'hklement/ubuntu-ruby:latest' }
+    docker_image { 'openhpi/co_execenv_ruby:2.5' }
     file_type { association :dot_rb, user: }
     help
-    name { 'Ruby 2.2' }
+    name { 'Ruby 2.5' }
     network_enabled { false }
     privileged_execution { false }
     permitted_execution_time { 10.seconds }