fixed incorrect usage of haskey for MvHistory in tests

Author: torfjelde

test/test_hparams.jl

@@ -102,5 +102,5 @@ end
         @info "x" val=3.0
     end
     hist = convert(MVHistory, lg)
-    @test haskey(hist, "x/val")
-end
+    @test haskey(hist, Symbol("x/val"))
+end