Unblock newer benchmark-ips versions

Mostly looking for 2.13.0's Ruby version output and 2.15.0's harmonic
mean fix.

Author: skipkayhil

msgpack.gemspec

@@ -37,5 +37,5 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'ruby_memcheck'
   s.add_development_dependency 'yard'
   s.add_development_dependency 'json'
-  s.add_development_dependency 'benchmark-ips', ['~> 2.10.0']
+  s.add_development_dependency 'benchmark-ips', ['~> 2.10']
 end