This commit changes sys.Wasm to sys.WASM, as requested on
https://groups.google.com/forum/#!topic/golang-dev/VquDxlhjPkg

Change-Id: I30a208c34576a8bb49b9beb524203d71df8fdf1c
Reviewed-on: https://go-review.googlesource.com/118395Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>