Fix typo

Author: devmotion

test/basekernels/constant.jl

@@ -26,7 +26,7 @@
         @test metric(ConstantKernel()) == KernelFunctions.Delta()
         @test metric(ConstantKernel(c=2.0)) == KernelFunctions.Delta()
         @test repr(k) == "Constant Kernel (c = $(c))"
-        test_params(kc, ([c],))
+        test_params(k, ([c],))
         test_ADs(c->ConstantKernel(c=first(c)), [c])
     end
 end