add wip cuke showing how to run a spec with the ruby command

- this passes against 2.6.4, but fails against the current code,
  probably related to #379
  (which turns out to be a dup of #14)

Author: dchelimsky

features/command_line/ruby.feature

@@ -0,0 +1,16 @@
+Feature: run with ruby command
+
+  @wip
+  Scenario:
+    Given a file named "example_spec.rb" with:
+      """
+      require 'rspec/autorun'
+
+      describe 1 do
+        it "is < 2" do
+          1.should be < 2
+        end
+      end
+      """
+    When I run `ruby example_spec.rb`
+    Then the output should contain "1 example, 0 failures"