Fix invalid interval warning

Before this change, following warnings printed during execution:
/usr/lib/ruby/vendor_ruby/puppet/parser/lexer.rb:250: warning: regexp has invalid interval
/usr/lib/ruby/vendor_ruby/puppet/parser/lexer.rb:250: warning: regexp has `}' without escape

I've only lightly tested this on ubuntu 12.04 with hiera 1.3.2 and puppet 3.4.3. The warnings no longer appear, and it still seems to work as expected.