Fix typo in core_types.rst

reference/core_types.rst

@@ -145,7 +145,7 @@ Godot provides also a set of common containers:
 -  Set
 -  Map
 
-The are very simple and aim to be as minimal as possible, as templates
+They are very simple and aim to be as minimal as possible, as templates
 in C++ are often inlined and make the binary size much fatter, both in
 debug symbols and code. List, Set and Map can be iterated using
 pointers, like this: