Add news entry for trilinear Upsample layer

Author: tknopp

NEWS.md

@@ -2,6 +2,7 @@
 
 ## v0.12.9
 * Fixed incorrect output and added GPU compatibility for [AlphaDropout](https://github.com/FluxML/Flux.jl/pull/1781).
+* Add trilinear [Upsample layer](https://github.com/FluxML/Flux.jl/pull/1792).
 
 ## v0.12.8
 * Optimized inference and gradient calculation of OneHotMatrix[pr](https://github.com/FluxML/Flux.jl/pull/1756)