Fix typo in curvature chapter (#263)

docs/chapters/curvature/content.en-GB.md

@@ -6,7 +6,7 @@ Problem solved!
 
 But, if we think about this a little more, this cannot possible work, because of something that you may have noticed in the section on [reordering curves](#reordering): what a curve looks like, and the function that draws that curve, are not in some kind of universal, fixed, one-to-one relation. If we have some quadratic curve, then simply by raising the curve order we can get corresponding cubic, quartic, and higher and higher mathematical expressions that all draw the _exact same curve_ but with wildly different derivatives. So: if we want to make a transition from one curve to the next look good, and we want to use the derivative, then we suddenly need to answer the question: "Which derivative?".
 
-How would you even decide? What makes the cubic derivatives better or less suited than, say, quintic derivatives? Wouldn't it be nicer if we could use something that was inherent to the curve, without being tied to the functions that yield that curve? And (of course) as it turns out, there is a way to define curvature in such a way that it only relies on what the curve actually looks like, and given where this section is in the larger body of this Primer, it should hopefully not be surprising that thee thing we can use to define curvature is the thing we talked about in the previous section: arc length.
+How would you even decide? What makes the cubic derivatives better or less suited than, say, quintic derivatives? Wouldn't it be nicer if we could use something that was inherent to the curve, without being tied to the functions that yield that curve? And (of course) as it turns out, there is a way to define curvature in such a way that it only relies on what the curve actually looks like, and given where this section is in the larger body of this Primer, it should hopefully not be surprising that the thing we can use to define curvature is the thing we talked about in the previous section: arc length.
 
 Intuitively, this should make sense, even if we have no idea what the maths would look like: if we travel some fixed distance along some curve, then the point at that distance is simply the point at that distance. It doesn't matter what function we used to draw the curve: once we know what the curve looks like, the function(s) used to draw it become irrelevant: a point a third along the full distance of the curve is simply the point a third along the distance of the curve.