Fix typo in polyfills path

Author: schlessera

features/install-wp-tests.feature

@@ -107,7 +107,7 @@ Feature: Scaffold install-wp-tests.sh tests
     When I run `composer install --no-interaction --working-dir=polyfills --quiet`
     Then the return code should be 0
 
-    When I run `WP_TESTS_DIR={RUN_DIR}/wordpress-tests-lib WP_TESTS_PHPUNIT_POLYFILLS_PATH={RUN_DIR}/polyfills/vendor/yoast/phunit-polyfills ./phpunit -c {PLUGIN_DIR}/hello-world/phpunit.xml.dist`
+    When I run `WP_TESTS_DIR={RUN_DIR}/wordpress-tests-lib WP_TESTS_PHPUNIT_POLYFILLS_PATH={RUN_DIR}/polyfills/vendor/yoast/phpunit-polyfills ./phpunit -c {PLUGIN_DIR}/hello-world/phpunit.xml.dist`
     Then the return code should be 0
 
     When I try `WP_TESTS_DIR={RUN_DIR}/wordpress-tests-lib WP_CORE_DIR={RUN_DIR}/wordpress /usr/bin/env bash {PLUGIN_DIR}/hello-world/bin/install-wp-tests.sh wp_cli_test_scaffold {DB_USER} {DB_PASSWORD} {DB_HOST} latest < affirmative-response`