fix android shadow on ActionButton.Item

[ahbo]

Was fixed in 2.7.1 but lost in the latest release...

[micnil]

The shadow style was set on the inner view in PR #212. In the pull request, @ghost says that he did this because the shadow prop caused a warning message (Which I assume is on IOS because I cannot see this message on android). In my PR #228 I did the exact same as here, but only for Android. It's not very beautiful, but I guess will solve both problems.

[ahbo]

@micnil I have no warning message (ios & android). Maybe it is related to some specific React-Native version.
For the platform select I recommand you to do the check inside the "shadowStyle" definition like this :
export const shadowStyle = { ...Platform.select({ android: { elevation: 5, }, ios: { shadowOpacity: 0.35, shadowOffset: { width: 0, height: 5 }, shadowColor: "#000", shadowRadius: 3, } }) };

Also the elevation value does not match to the material design guidelines.
https://material.io/guidelines/material-design/elevation-shadows.html#elevation-shadows-elevation-android
Resting elevation > Floating action button (FAB - resting elevation) > Elevation = 6dp

[mastermoo]

closing this pr in favor of #228