fix empty(::LittleDict)

The old version just called `LittleDict{K, V}()`, but that may not be
an accurate empty version of the type passed. This now calls empty on
the keys and values seperately.

Author: Tokazama

src/little_dict.jl

@@ -183,7 +183,9 @@ function merge(
 end
 
 
-Base.empty(dd::LittleDict{K,V}) where {K,V} = LittleDict{K,V}()
+function Base.empty(dd::LittleDict{K,V}) where {K,V}
+    LittleDict{K, V}(empty(getfield(dd, :keys)), empty(getfield(dd, :vals)))
+end
 
 ######## Methods that all mutable AbstractDict's should implement