Tighten constraint on childprocess gem

The constraint in 48911e7 was a bit too loose, considering this gem has
not reached 1.0, and so we can't rely on semantic versioning just yet.

Change-Id: Ife7a86cd6aae6b54b7ed516870cf8770fe3f07d0
Reviewed-on: http://gerrit.causes.com/46997
Tested-by: jenkins <jenkins@brigade.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>

Author: sds

overcommit.gemspec

@@ -26,7 +26,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = '>= 1.9.3'
 
-  s.add_dependency             'childprocess', '~> 0.5'
+  s.add_dependency             'childprocess', '~> 0.5.0'
 
   s.add_development_dependency 'image_optim', '~> 0.20.0'
   s.add_development_dependency 'rspec', '~> 3.0'