Log Message:
Update to 2.000018

Upstream changes:
2.000018 - 2015-10-29
 - repair CPAN.pm bootstrapping broken by extraneous prerequisite.
 - ensure directories are created in correct order to avoid errors

2.000017 - 2015-10-06
 - fix shell quoting for fish shell
 - work around issue where some cpanm versions wouldn't upgrade
   ExtUtils::MakeMaker in some cases it should have
 - added --quiet option to surpress directory creation message
 - build_environment_vars_for, build_activate_environment_vars_for, and
   environment_vars_string_for options will always include directories being
   added, even if they were already in current ENV vars
 - fixes for author tests
 - create directory structure under created local::libs, ensuring arch dirs
   will always be added to @INC by perl
 - only cause CPAN.pm to prefer ExtUtils::MakeMaker over Module::Build during
   bootstrap process, not after
 - bootstrap process refactored