Update docs/src/maths/propagators.md

Co-authored-by: Anthony Blaom, PhD <[email protected]>

Author: oxinabox

docs/src/maths/propagators.md

@@ -191,7 +191,7 @@ end
 function ChainRulesCore.rrule(m::Multiplier, y)
     product = m(y)
     function pullback(Δproduct) 
-        ∂self = Tangent{typeof(m)}(; x = Δproduct * y')
+        ∂self = Tangent{Multiplier}(; x = Δproduct * y')
         ∂y = m.x' * Δproduct
         return ∂self, ∂y
     end