options for have_tag should also support Regexp

For backwards compatibility with RSpec 1.x, have_tag should also allow Regexp as the second parameter.
e.g. "<h1>Title</h1>".should have_tag("h1", /itl/)
See http://old.rspec.info/rails/writing/views.html
specs for unnamed Regexp argument
0.4.4 version
modern gemspec