revert version branch

Author: st--

test/chainrules.jl

@@ -21,13 +21,7 @@
     compare_gradient(:Zygote, [x, y]) do xy
         KernelFunctions.Sinus(r)(xy[1], xy[2])
     end
-    if VERSION < v"1.6"
-        compare_gradient(:ForwardDiff, [Q, x, y]) do Qxy
-            SqMahalanobis(Qxy[1]; skipchecks=true)(Qxy[2], Qxy[3])
-        end
-    else
-        compare_gradient(:Zygote, [Q, x, y]) do Qxy
-            SqMahalanobis(Qxy[1])(Qxy[2], Qxy[3])
-        end
+    compare_gradient(:Zygote, [Q, x, y]) do Qxy
+        SqMahalanobis(Qxy[1])(Qxy[2], Qxy[3])
     end
 end