Fix cucumber step 'it should pass|fail with exactly:'

This fixes the failure message of the output comparison so that it shows
the correct diff.

features/03_testing_frameworks/cucumber/steps/command/check_output_of_command.feature

@@ -327,6 +327,38 @@ Feature: All output of commands which were executed
     When I run `cucumber`
     Then the features should all pass
 
+  Scenario: Match passing exit status but fail to match exact output
+    Given an executable named "bin/aruba-test-cli" with:
+    """bash
+    #!/usr/bin/env bash
+
+    echo -ne "hello\nworld"
+    exit 0
+    """
+    And a file named "features/output.feature" with:
+    """cucumber
+    Feature: Run command
+      Scenario: Run command
+        When I run `aruba-test-cli`
+        Then it should pass with exactly:
+        \"\"\"
+        hello
+        worl
+        \"\"\"
+    """
+    When I run `cucumber`
+    Then the features should not pass with:
+    """
+          expected "hello
+    world" to output string is eq: "hello
+    worl"
+          Diff:
+          @@ -1,3 +1,3 @@
+           hello
+          -worl
+          +world
+    """
+
   Scenario: Match failing exit status and partial output
     Given an executable named "bin/aruba-test-cli" with:
     """bash

lib/aruba/cucumber/command.rb

@@ -423,7 +423,7 @@
     expect(last_command_stopped).not_to be_successfully_executed
   end
 
-  expect(last_command_stopped).to have_output an_output_string_being_eq(expected)
+  expect(last_command_stopped.output).to output_string_eq(expected)
 end
 
 Then(/^it should not (pass|fail) (?:with regexp?|matching):$/) do |pass_fail, expected|