fix displacement logger ref

Author: ejmeitz

docs/src/documentation.md

@@ -1115,7 +1115,7 @@ The available loggers are:
 - [`GeneralObservableLogger`](@ref)
 - [`TemperatureLogger`](@ref)
 - [`CoordinatesLogger`](@ref)
-- [`DisplacementLogger`](@ref)
+- [`DisplacementsLogger`](@ref)
 - [`VelocitiesLogger`](@ref)
 - [`TotalEnergyLogger`](@ref)
 - [`KineticEnergyLogger`](@ref)