Improve code formatting

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: simsurace

test/basekernels/periodic.jl

@@ -15,6 +15,6 @@
     TestUtils.test_interface(PeriodicKernel(; r=[0.9, 0.9]), ColVecs{Float64})
     TestUtils.test_interface(PeriodicKernel(; r=[0.8, 0.7]), RowVecs{Float64})
 
-    test_ADs(r -> PeriodicKernel(r = exp.(r)), log.(r))
+    test_ADs(r -> PeriodicKernel(; r=exp.(r)), log.(r))
     test_params(k, (r,))
 end