Pin childprocess on older Rubies

Author: JonRowe

Gemfile

@@ -63,8 +63,10 @@ if RUBY_VERSION < '2.3.0' && !!(RbConfig::CONFIG['host_os'] =~ /cygwin|mswin|min
   gem "childprocess", "< 1.0.0"
 elsif RUBY_VERSION < '2.0.0'
   gem "childprocess", "< 1.0.0"
+elsif RUBY_VERSION < '2.3.0'
+  gem "childprocess", "< 3.0.0"
 else
-  gem "childprocess", "> 1.0.0"
+  gem "childprocess", ">= 3.0.0"
 end
 
 platforms :jruby do