Wrong arch guessed in tools downloads

See Ben's [comment on spring.io blog](https://spring.io/blog/2014/07/11/spring-tool-suite-and-groovy-grails-tool-suite-3-6-0-released#comment-1500477476) and this [SO question](https://stackoverflow.com/questions/19877924/what-is-the-list-of-possible-values-for-navigator-platform-as-of-today) on why 64-bit architecture isn't correctly advertised by browsers.