Fix typos "probabilty", "dot project"

Resolves RayTracing#1607

Author: hollasch

books/RayTracingInOneWeekend.html

@@ -2895,7 +2895,7 @@
 glass materials) can also vary with incident viewing direction (the direction of the incoming ray).
 
 Lambertian (diffuse) reflectance can either always scatter and attenuate light according to its
-reflectance $R$, or it can sometimes scatter (with probabilty $1-R$) with no attenuation (where a
+reflectance $R$, or it can sometimes scatter (with probability $1-R$) with no attenuation (where a
 ray that isn't scattered is just absorbed into the material). It could also be a mixture of both
 those strategies. We will choose to always scatter, so implementing Lambertian materials becomes a
 simple task:
@@ -3000,8 +3000,8 @@
 The reflected ray direction in red is just $\mathbf{v} + 2\mathbf{b}$. In our design, $\mathbf{n}$
 is a unit vector (length one), but $\mathbf{v}$ may not be. To get the vector $\mathbf{b}$, we scale
 the normal vector by the length of the projection of $\mathbf{v}$ onto $\mathbf{n}$, which is given
-by the dot project $\mathbf{v} \cdot \mathbf{n}$. (If $\mathbf{n}$ were not a unit vector, we would
-also need to divide this dot project by the length of $\mathbf{n}$.) Finally, because $\mathbf{v}$
+by the dot product $\mathbf{v} \cdot \mathbf{n}$. (If $\mathbf{n}$ were not a unit vector, we would
+also need to divide this dot product by the length of $\mathbf{n}$.) Finally, because $\mathbf{v}$
 points _into_ the surface, and we want $\mathbf{b}$ to point _out_ of the surface, we need to negate
 this projection length.