doc/go1.11: clarify GOOS/GOARCH pair of WebAssembly port

It's more common to specify GOOS/GOARCH values in that order,
rather than the inverse. Fix the order.

Updates #18892.

Change-Id: I8551508599e019f6617dc007397b562c9926418d
Reviewed-on: https://go-review.googlesource.com/120057
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

doc/go1.11.html

@@ -55,7 +55,7 @@ <h2 id="ports">Ports</h2>
 
 <h3 id="wasm">WebAssembly</h3>
 <p>
-  Go 1.11 adds an experimental port to WebAssembly (<code>wasm/js</code>).
+  Go 1.11 adds an experimental port to WebAssembly (<code>js/wasm</code>).
 </p>
 
 <h2 id="library">Core library</h2>