Use Oracle enhanced adapter `release52` to support Rails `5-2-stable`

Gemfile

@@ -162,7 +162,7 @@ if ENV["ORACLE_ENHANCED"]
   platforms :ruby do
     gem "ruby-oci8", "~> 2.2"
   end
-  gem "activerecord-oracle_enhanced-adapter", github: "rsim/oracle-enhanced", branch: "master"
+  gem "activerecord-oracle_enhanced-adapter", github: "rsim/oracle-enhanced", branch: "release52"
 end
 
 # A gem necessary for Active Record tests with IBM DB.