Docs for arc: origin -> center

Issue description

The description has the following sentence:

"The origin of the arc's ellipse may be changed with the ellipseMode() function. "

This should be:

"The center of the arc's ellipse may be changed with the ellipseMode() function. "

The word "center" is used for ellipses. The word "origin" is used for coordinate systems.
Reference: https://en.wikipedia.org/wiki/Ellipse

URL(s) of affected page(s)

https://processing.org/reference/arc_.html

Proposed fix

Replace "origin" with "center".

https://processing.org/reference/arc_.html の対象となる arc リファレンスページを開き、楕円の原点を説明している文を見つけます。提案どおり “origin” を “center” に置き換え、その後、表現が正しいことを確認するためにレンダリングされたページを確認します。