Fix tests for Travis CI

Author: jakeNiemiec

test/rake_tasks_test.rb

@@ -53,12 +53,12 @@ def test_rake_webpacker_yarn_install_in_production_environment
   end
 
   def test_check_node_version
-    output = Dir.chdir(test_app_path) { `rake webpacker:check_node 2>&1` }
+    output = Dir.chdir(test_app_path) { `bundle exec rake webpacker:check_node 2>&1` }
     assert_empty output
   end
 
   def test_check_yarn_version
-    output = Dir.chdir(test_app_path) { `rake webpacker:check_yarn 2>&1` }
+    output = Dir.chdir(test_app_path) { `bundle exec rake webpacker:check_yarn 2>&1` }
     assert_empty output
   end