Update index.md

Fixed a typo.

Author: pitmonticone

docs/src/index.md

@@ -5,7 +5,7 @@ It aims at providing a flexible framework for creating kernels and manipulating
 The main goals of this package are:
 - **Flexibility**: operations between kernels should be fluid and easy without breaking.
 - **Plug-and-play**: including the kernels before/after other steps should be straightforward.
-- **Automatic Differentation** compatibility: all kernel functions which _ought_ to be differentiable using AD packages like [ForwardDiff.jl](https://github.com/JuliaDiff/ForwardDiff.jl) or [Zygote.jl](https://github.com/FluxML/Zygote.jl) _should_ be.
+- **Automatic Differentation compatibility**: all kernel functions which _ought_ to be differentiable using AD packages like [ForwardDiff.jl](https://github.com/JuliaDiff/ForwardDiff.jl) or [Zygote.jl](https://github.com/FluxML/Zygote.jl) _should_ be.
 
 This package builds on top of lots of excellent existing work in packages such as [MLKernels.jl](https://github.com/trthatcher/MLKernels.jl), [Stheno.jl](https://github.com/willtebbutt/Stheno.jl), [GaussianProcesses.jl](https://github.com/STOR-i/GaussianProcesses.jl), and [AugmentedGaussianProcesses.jl](https://github.com/theogf/AugmentedGaussianProcesses.jl).