Don't require capacity parameter for Dictionary.

src/Collections/Dictionary.hpp

@@ -11,6 +11,7 @@ namespace Arbutils::Collections {
         using iterator = typename std::unordered_map<KeyT, ValueT, std::hash<KeyT>, std::equal_to<KeyT>,
                                                      std::allocator<std::pair<const KeyT, ValueT>>>::iterator;
     public:
+        Dictionary() : _map() {}
         explicit Dictionary(size_t capacity) : _map(capacity) {}
         explicit Dictionary(const std::initializer_list<std::pair<const KeyT, ValueT>>& l) : _map(l){}