- Update requirements in readme and Rakefile/hoe spec.

Remove plans for a post_install_message from Rakefile.

[git-p4: depot-paths = "//src/minitest/dev/": change = 12323]

README.rdoc

@@ -714,8 +714,7 @@ Authors... Please send me a pull request with a description of your minitest ext
 
 == REQUIREMENTS:
 
-* Ruby 1.8.7+. No magic is involved. I hope.
-* NOTE: 1.8 and 1.9 will be dropped in minitest 6+.
+* Ruby 2.3+. No magic is involved. I hope.
 
 == INSTALL:
 

Rakefile

@@ -11,21 +11,7 @@ Hoe.spec "minitest" do
 
   license "MIT"
 
-  ## TODO: uncomment this on the last point release on 5.x
-  #
-  #   self.post_install_message = <<-"EOM"
-  # NOTE: minitest 5 will be the last in the minitest family to support
-  #       ruby 1.8 and 1.9 (and maybe 2.0?). If you need to keep using 1.8
-  #       or 1.9, you need to pin your dependency to minitest with
-  #       something like "~> 5.0".
-  #
-  #       Further, minitest 6 will be dropping the following:
-  #
-  #       + MiniTest (it's been Minitest for *years*)
-  #       + MiniTest::Unit
-  #       + MiniTest::Unit::TestCase
-  #       + assert_send (unless you argue for it well)
-  #   EOM
+  require_ruby_version "~> 2.3"
 end
 
 desc "Find missing expectations"