Use the global and report-specific options for notifyReleaseStages
Use the global and report-specific options for notifyReleaseStages

Prefer the report-specific option but fall back to the global option
when the report-specific one is not set.

Fixes #66
bugsnag/bugsnag-cocoa,bugsnag/bugsnag-cocoa,bugsnag/bugsnag-cocoa,bugsnag/bugsnag-cocoa