UIButton image and UILabel text do not get removed when skeleton is shown in iOS 12 and iOS 11.

Description

UIButton image and UILabel text does not get removed when skeleton is shown in iOS 12 and iOS 11. The text and the button image are unseen when skeleton view is shown on iOS 13 and above.

What type of issue is this? (place an `x` in one of the `[ ]`)

[X] bug
[ ] enhancement (feature request)
[ ] question
[ ] documentation related
[ ] discussion

Requirements (place an `x` in each of the `[ ]`)

[X] I've read and understood the Contributing guidelines and have done my best effort to follow them.
[X] I've read and agree to the Code of Conduct.
[X] I've searched for any related issues and avoided creating a duplicate issue.

Bug Report

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SkeletonView Environment:

SkeletonView version: 1.29.2 Xcode version: 13.2.1 Swift version: 5.3

Steps to reproduce:

Please replace this with the steps to reproduce the behavior. Scenario A:

Create a UILabel with a text
Trigger showAnimatedGradientSkeleton (showSkeleton and showAnimatedSkeleton can also be used to replicate the bug)
Run in iOS 12 or iOS 11.

Scenario B: Alternatively you can,

Create a UIButton and set an image instead of a title
Trigger showAnimatedGradientSkeleton
Run in iOS 12 and iOS 11

Expected result:

Scenario A: Text should be not seen from UILabel when skeleton is shown.

Scenario B: Button image should be not seen from the UIButton when skeleton is shown.

Actual result:

Scenario A: Text is seen in UILabel when skeleton is shown. The following screenshot is taken while the skeleton gradient is animating:

Scenario B: Button image is seen in the UIButton when skeleton is shown. The following screenshot is taken while the skeleton gradient is animating:

Juanpe / SkeletonView