Bump Xcode to 9.1 and test against iOS 8.1 and 9.0 (close #325)
Bump Xcode to 9.1 and test against iOS 8.1 and 9.0 (close #325)

snowplow/snowplow-objc-tracker,snowplow/snowplow-objc-tracker,snowplow/snowplow-objc-tracker,snowplow/snowplow-objc-tracker