Remove use of Location#getTime or bump min API

[sarahcodes100]

We should not be using Location#getTime for elapsed time computation but are doing so for earlier versions of Android because Location#getElapsedRealtimeNano is not available.

https://github.com/mapzen/lost/blob/master/lost/src/main/java/com/mapzen/android/lost/internal/SystemClock.java#L13-L19 https://developer.android.com/reference/android/location/Location.html#getElapsedRealtimeNanos()

Consider creating another, reliable way to compute this value or modifying LOST to workaround this while still respecting LocationRequest#fastestInterval. Alternatively, evaluate bumping the minimum SDK required from 15 to 17 (this would drop support for 3% of users).