ScreenInfo.Density has wrong type

[jakekdodd]

The Density field on the ScreenInfo struct is typed as an int, but in reality this is often a floating-point value. I believe this was mistyped because the example in the Common Fields spec is—only by coincidence—a whole number.

This leads to json marshaling/unmarshaling errors at runtime:

WARN[0042] error decoding payloadjson: cannot unmarshal number 2.75 into Go struct field ScreenInfo.context.screen.density of type int