Fix fraction line thickness for vector output.
Fix fraction line thickness for vector output.

It was a mistake to store the thickness in an int variable.

janmarthedal/mathml2svg,gjtorikian/lasem,wavewave/lasem,wavewave/lasem,wavewave/lasem,gjtorikian/lasem,janmarthedal/mathml2svg,gjtorikian/lasem,janmarthedal/mathml2svg,wavewave/lasem,gjtorikian/lasem,janmarthedal/mathml2svg