Fixed torus tip.

Library/tips.json

 {"tips":[
 "Filling a non-regular hole of valence <i>n</i> in a cubic manifold B-spline with <i>n</i> bicubic Bezier patches with <i>G<sup>1</sup></i> continuity is impossible in general if <i>n</i> is even.",
-"A closed, regular quad mesh is a torus."
+"A closed, regular quad mesh is a topological torus."
 ]}