[Spec] Fix bounds check prose for array.fill and array.copy

The prose incorrectly used "larger than or equal to" when it should have used
just "larger than." The formalism was already correct.

Fixes #536.

document/core/exec/instructions.rst

@@ -1065,7 +1065,7 @@ Reference Instructions
 
 12. Assert: due to :ref:`validation <valid-array.fill>`, the :ref:`array instance <syntax-arrayinst>` :math:`S.\SARRAYS[a]` exists.
 
-13. If :math:`d + n` is larger than or equal to the length of :math:`S.\SARRAYS[a].\AIFIELDS`, then:
+13. If :math:`d + n` is larger than the length of :math:`S.\SARRAYS[a].\AIFIELDS`, then:
 
     a. Trap.
 
@@ -1175,11 +1175,11 @@ Reference Instructions
 
 23. Assert: due to :ref:`validation <valid-array.copy>`, the :ref:`array instance <syntax-arrayinst>` :math:`S.\SARRAYS[a_2]` exists.
 
-24. If :math:`d + n` is larger than or equal to the length of :math:`S.\SARRAYS[a_1].\AIFIELDS`, then:
+24. If :math:`d + n` is larger than the length of :math:`S.\SARRAYS[a_1].\AIFIELDS`, then:
 
     a. Trap.
 
-25. If :math:`s + n` is larger than or equal to the length of :math:`S.\SARRAYS[a_2].\AIFIELDS`, then:
+25. If :math:`s + n` is larger than the length of :math:`S.\SARRAYS[a_2].\AIFIELDS`, then:
 
     a. Trap.