Update Discard + Paranoia gem installation

Gemfile

@@ -26,9 +26,18 @@ group :development, :test do
   gem "awesome_print"
   gem "timecop"
 
-  # to test the integration
-  gem "discard"
-  gem "paranoia"
+  # To test integrations
+
+  # Both the paranoia and discard integrations require Rails > 4.2
+  # Actually parsing the resolved rails version is complicated, so
+  # we're basing this on the incompatible Rails version strings from
+  # .travis.yml
+
+  unless ['~> 3.2.0', '~> 4.0.0', '~> 4.1.0'].include?(rails)
+    gem "discard"
+    gem "paranoia"
+  end
+
   if RUBY_VERSION < "2.3.0"
     gem "paper_trail", "< 9.0.0"
   else

README.md

@@ -315,9 +315,12 @@ Manually populating counter caches with dynamically over-written foreign keys (`
 
 ### Soft-deletes with `paranoia` or `discard`
 
-This gem will keep counters correctly updated when using
-[paranoia](https://github.com/rubysherpas/paranoia) or [discard](https://github.com/jhawthorn/discard) for soft-delete support. However, to ensure that counts are incremented after a
-restore you have to make sure that the to set up soft deletion (via `acts_as_paranoid` or `include Discard::Model`) before the call to `counter_culture` in your model:
+This gem will keep counters correctly updated in Rails 4.2 or later when using
+[paranoia](https://github.com/rubysherpas/paranoia) or
+[discard](https://github.com/jhawthorn/discard) for soft-delete support.
+However, to ensure that counts are incremented after a restore you have
+to make sure that the to set up soft deletion (via `acts_as_paranoid` or
+`include Discard::Model`) before the call to `counter_culture` in your model:
 
 #### Paranoia