add \idotsint

[Wyatt915]

MathML output from MathJax (\idotsint_{a}^{b})

<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
  <mo data-mjx-texclass="OP">&#x222B;</mo>
  <mo>&#x22EF;</mo>
  <msubsup>
    <mo data-mjx-texclass="OP">&#x222B;</mo>
    <mrow data-mjx-texclass="ORD">
      <mi>a</mi>
    </mrow>
    <mrow data-mjx-texclass="ORD">
      <mi>b</mi>
    </mrow>
  </msubsup>
</math>

note that only the final integral is part of the <msubsup> expression