feat(Visibility): add fireOnMount

[layershifter]

Fixes #1911.

[codecov-io]

Codecov Report

Merging #2018 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2018      +/-   ##
==========================================
+ Coverage   99.76%   99.76%   +<.01%     
==========================================
  Files         148      148              
  Lines        2556     2557       +1     
==========================================
+ Hits         2550     2551       +1     
  Misses          6        6

Impacted Files	Coverage Δ
src/behaviors/Visibility/Visibility.js	100% <100%> (ø)	⬆️

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[levithomason]

Made a small verbiage tweak, will merge on pass.

[levithomason]

Released in [email protected]

[boostup]

Hello Guys!

I'm basically trying to show a react element that is onScreen on first render. So, I found Visibility: onOnScreen doesn't fire if element is onScreen on first render, which lead me to this page here.

1)According to the comment on this page on Sep 11, a fix was released at version 0.73.0
I have version 0.76.0 in my project. However, when wrapping it with a Visibility react tag, an element, say an image, does not show it until I scroll even though the image is already partially onScreen.

2)Also, if I include the fireOnMount prop on the Visibility tag, then calculations.onScreen is always equal to true. Is that normal? I can't understand the reason for this...What is fireOnMount for? I don't get it from the docs https://semantic-ui.com/behaviors/visibility or https://react.semantic-ui.com/behaviors/visibility

Here is a codesandbox: https://codesandbox.io/s/nr5k9k6zwp

Thanks for any assistance on these 2 points

[layershifter]

If you want to get help, you should create a new issue and fully fill issue template.