proposal: sub should be return original object for chaining

[Slava Bereza]

buttonBuyAnnualPriceOffset
  .sub(buttonBuyAnnualTextWidth, (v, width) => {
    return width > v ? width : v
  })
  .sub(buttonBuyAnnualTextWidth, (v, width) => {
    return width > v ? width : v
  })
  ;

[Slava Bereza]

The "sub" renamed to "update.by" and returns the chaining self context
0.6.0