gemfile reworked to work on old ruby versions

Gemfile

@@ -3,15 +3,19 @@ source "http://rubygems.org"
 # @param [Array<String>] versions compatible ruby versions
 # @return [Array<String>] an array with mri platforms of given versions
 def mries(*versions)
-  versions.flat_map do |v|
-    %w(ruby mingw x64_mingw)
-        .map { |platform| "#{platform}_#{v}".to_sym unless platform == "x64_mingw" && v < "2.0" }
-        .delete_if &:nil?
-  end
+  versions.map do |v|
+    %w(ruby mingw x64_mingw).map do |platform|
+      "#{platform}_#{v}".to_sym unless platform == "x64_mingw" && v < "2.0"
+    end.delete_if &:nil?
+  end.flatten
+end
+
+gem "ruby-debug-base", :platforms =>  [:jruby, *mries('18')]
+
+if RUBY_VERSION && RUBY_VERSION >= "1.9"
+  gem "ruby-debug-base19x", ">= 0.11.32", :platforms => mries('19')
 end
 
-gem "ruby-debug-base", :platforms => [:jruby, *mries('18')]
-gem "ruby-debug-base19x", ">= 0.11.32", :platforms => mries('19')
 if RUBY_VERSION && RUBY_VERSION >= "2.0"
   gem "debase", "~> 0.2", ">= 0.2.2", :platforms => mries('20', '21', '22', '23', '24', '25')
 end
@@ -23,6 +27,10 @@ group :development do
 end
 
 group :test do
-  gem "test-unit"
+  if RUBY_VERSION < "1.9"
+    gem "test-unit", "~> 2.1.2"
+  else
+    gem "test-unit"
+  end
 end