Mark the reporter as public api

Changelog.md

@@ -7,6 +7,8 @@ Enhancements:
   bit of memory. (Myron Marston, #2172)
 * Apply hooks registered with `config` to previously defined groups.
   (Myron Marston, #2189)
+* `RSpec::Core::Configuration#reporter` is now public API under semver.
+  (Jon Rowe, #2193)
 
 ### 3.5.0.beta1 / 2016-02-06
 [Full Changelog](http://github.com/rspec/rspec-core/compare/v3.4.3...v3.5.0.beta1)

lib/rspec/core/configuration.rb

@@ -825,7 +825,7 @@ def play_onto(reporter)
         end
       end
 
-      # @private
+      # @return [RSpec::Core::Reporter] the currently configured reporter
       def reporter
         # @reporter_buffer should only ever be set in this method to cover
         # initialization of @reporter.