Fix typo in panner-distance-clampling.html test

The should.throw() method now expects an actual error object instead
of a string and I think someone just forgot to change the
'RangeError' strings in this test to be just the RangeError object.

Bug: 865371
Test: test passes again
Change-Id: I07cc057ff4f608a01ed3f35a0268b6e267078d13
Reviewed-on: https://chromium-review.googlesource.com/1144128
Reviewed-by: Robert Ma <robertma@chromium.org>
Reviewed-by: Hongchan Choi <hongchan@chromium.org>
Commit-Queue: Raymond Toy <rtoy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576856}
6 files changed