Fix typo in global instance invariant

Author: ia0

document/core/exec/runtime.rst

@@ -325,7 +325,7 @@ It records its :ref:`type <syntax-globaltype>` and holds an individual :ref:`val
 
 The value of mutable globals can be mutated through :ref:`variable instructions <syntax-instr-variable>` or by external means provided by the :ref:`embedder <embedder>`.
 
-It is an invariant of the semantics that the value has a type equal to the :ref:`value type <syntax-valtype>` of :math:`\globaltype`.
+It is an invariant of the semantics that the value has a type equal to the value type of :math:`\valtype`.
 
 
 .. index:: ! element instance, element segment, embedder, element expression