Bump up spray to version 1.3.2

Since spray has now released 1.3.2, let's bump up the version to use it rather than the snapshot versions.

@sclasen Do you think this is the right time to release a new version of spray-aws as well? There are several feature improvements since last spray-aws version which only the dependency on non-stable spray release stopped us from using. Maybe more users had similar worries.