Fix comparison warning (#147)
Fix comparison warning (#147)

After changing the deployment target for the library to 6.0,
`UIApplicationUserDidTakeScreenshotNotification` was not guaranteed to
be available anymore. However, if a project's deployment target is set
to 8.0 (which _does_ guarantee the presence of the symbol) this leads to
a warning in Xcode.
bugsnag/bugsnag-cocoa,bugsnag/bugsnag-cocoa,bugsnag/bugsnag-cocoa,bugsnag/bugsnag-cocoa