[js-api] Throw RangeError when getArg's index is out of bounds (#196)

Closes #184.

Author: aheejin

document/js-api/index.bs

@@ -1310,7 +1310,7 @@ The <dfn method for="Exception">getArg(|exceptionTag|, |index|)</dfn> method ste
     1. Throw a {{TypeError}}.
 1. Let |payload| be **this**.\[[Payload]].
 1. If |index| ≥ |payload|'s [=list/size=],
-    1. Throw a {{TypeError}}.
+    1. Throw a {{RangeError}}.
 1. Return [=ToJSValue=](|payload|[|index|]).
 
 </div>

test/js-api/exception/getArg.tentative.any.js

@@ -43,7 +43,7 @@ test(() => {
   const tag = new WebAssembly.Tag({ parameters: [] });
   const exn = new WebAssembly.Exception(tag, []);
   for (const value of outOfRangeValues) {
-    assert_throws_js(TypeError, () => exn.getArg(tag, value));
+    assert_throws_js(RangeError, () => exn.getArg(tag, value));
   }
 }, "Getting out-of-range argument");