gemspec: support rdoc 5.x

rdoc 5.x does not introduce incompatible changes outside
of dropping Ruby 1.8 support.  We never actually supported
Ruby 1.8, either(*), so formalize that in the gemspec while
we're at it.

1 files changed, 1 insertions, 1 deletions

diff --git a/lib/rdoc/discover.rb b/lib/rdoc/discover.rb
index 9450f42..30c5ae2 100644
--- a/lib/rdoc/discover.rb
+++ b/lib/rdoc/discover.rb
@@ -1,6 +1,6 @@
 # :stopdoc:
 begin
-  gem 'rdoc', '~> 4.1'
+  gem 'rdoc', [ '>= 4.2', '< 6.0' ]
   require_relative '../olddoc'
 rescue Gem::LoadError
 end unless defined?(Olddoc)