graphics/dataplot: Fix distinfo after r508362

> usnistgov-dataplot-20190426-7236db0_GH0.tar.gz is not in /usr/ports/graphics/dataplot/distinfo.

> Either /usr/ports/graphics/dataplot/distinfo is out of date, or

> usnistgov-dataplot-20190426-7236db0_GH0.tar.gz is spelled incorrectly.

• Error code 1

Pointy hat: pfg