Gemspec: advanced adapter 1.5, activerecord ~> 1.4

Declare support for oracle advanced adapter 1.5.x and activerecord 1.4.x
gemspec: advanced adapter 1.5, activerecord ~> 1.4

Declare compatibility with oracle advanced adapter 1.5.x and activerecord 1.4.x
Merge pull request #62 from rsim/bump-up-dependency-advanced-adapter-to-1.5-activerecord-4.1

Declare compatibility with advanced adapter to 1.5.x and activerecord to 4.1.x