[eqn] Incorrect approx symbol

[Nguyễn Gia Phong via discussion of the GNU roff typesetting system and related software]

Hi,

At least for MathML, eqn output does not seem right for approx:

$ printf '.EQ\napprox\n.EN\n' | ./eqn -TMathML
.do if !dEQ .ds EQ
.do if !dEN .ds EN
.EQ
<math><mtext>\(~=</mtext></math>
.EN

Kind regards,
Phong