Merge pull request #22 from jhuangtw-dev/relax-pg-version-req

update pg gem version requirement to ~> 0.18.0

Author: toothrot

postgres_to_redshift.gemspec

@@ -20,6 +20,6 @@ Gem::Specification.new do |spec|
 
   spec.add_development_dependency "bundler", "~> 1.6"
   spec.add_development_dependency "rake", "~> 10.0"
-  spec.add_dependency "pg", "~> 0.17.0"
+  spec.add_dependency "pg", "~> 0.18.0"
   spec.add_dependency "aws-sdk-v1", "~> 1.54"
 end