make dot docstring match the implementation

Author: adienes

src/generic.jl

@@ -938,7 +938,7 @@ vector is conjugated.
 `dot` also works on arbitrary iterable objects, including arrays of any dimension,
 as long as `dot` is defined on the elements.
 
-`dot` is semantically equivalent to `sum(dot(vx,vy) for (vx,vy) in zip(x, y))`,
+`dot` is semantically equivalent to `reduce(+, dot(vx,vy) for (vx,vy) in zip(x, y))`,
 with the added restriction that the arguments must have equal lengths.
 
 `x ⋅ y` (where `⋅` can be typed by tab-completing `\\cdot` in the REPL) is a synonym for