Clean up plus sign spacing in documentation page

[amrhassab]

Minor clean-up to keep the documentation page crisp, clear, and consistent.

For example at https://animejs.com/documentation/#change

progressLogEl.value = 'progress : '+Math.round(anim.progress)+'%';

does not follow the same spacing as

changeLogEl.value = 'changes : ' + changes;

now:
progressLogEl.value = 'progress : ' + Math.round(anim.progress) + '%';

Other similar examples were also changed

[juliangarnier]

Thanks for the PR, I'm closing since the docs have been completely rewritten.