Ruby » Ruby master

test_gem_installer.rb: fix a test failure

• test/rubygems/test_gem_installer.rb (test_install_extension_flat):
  use ruby in build directory in case ruby is not installed.
  [ruby-core:53265] [Bug #8058]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@41600 b2dd03c8-39d4-4d8f-98ff-823fe69b080e