Wrong int32 min-max range definition on numTypes.lua (#5031)

* Update numTypes.lua

int32 range was wrongly defined.

* Update numTypes.lua

Fix number 32 to 31

lua/flatbuffers/numTypes.lua

@@ -119,8 +119,8 @@ local int16_mt =
 local int32_mt = 
 {
     bytewidth = 4,
-    min_value = -2^15,
-    max_value = 2^15-1,
+    min_value = -2^31,
+    max_value = 2^31-1,
     lua_type = type(1),
     name = "int32",
     packFmt = "<i4"