Hush method return type warnings when importing SUUpdater.h

Just a small semantic issue.

When including SUUpdater.h in projects with a warning level set to -Wextra warnings are generated because - delegate and - initForBundle: have no return type specified.

Clang seems to have a sweet spot with -Wall and -Wextra so it would be nice to be able to include Sparkle in a project without it generating any additional warning noise.

http://programmers.stackexchange.com/questions/122608/clang-warning-flags-for-objective-c-development