Don't use Bash extended redirect syntax

"&>PATH" is Bash extended redirect syntax.

See also: http://www.gnu.org/software/bash/manual/bashref.html#Redirecting-Standard-Output-and-Standard-Error

It is not worked well on normal sh such as dash. dash is the /bin/sh
on Debian GNU/Linux. If dash is used for "system", "gem install ..."
is run in background. "system" for background command always returns
true:

    % ruby -e 'p system("nonexsitent &")'
    true
    sh: 1: nonexsitent: not found
    % ruby -e 'p system("nonexsitent")'
    nil

It means "install_gem" always returns true. It breaks the following
logic in lib/hoe/deps.rb:

    install_gem("hoe-#{name}", version, false) or
      install_gem(name, version, false) or
      install_gem(dash_name, version, false) or
      warn "could not install gem for #{name} plugin"

It causes a problem for "kpeg" gem. "hoe-kpeg" gem doesn't
exist. "kpeg" gem should be searched as fallback but it is not
searched. Because install_gem("hoe-#{name}") is not failed.

RDoc depends on "kpeg". So "rake newb" for RDoc is failed.