playground: update favicon.ico to be consistent with the website

The two got out of sync with commit https://golang.org/cl/26850

Before:
$ identify app/static/favicon.ico
app/static/favicon.ico ICO 16x16 16x16+0+0 32-bit DirectClass 1.15KB 0.000u 0:00.000

Change:
$ cp ../go/favicon.ico app/static/favicon.ico

After:
$ identify app/static/favicon.ico
app/static/favicon.ico[0] ICO 32x32 32x32+0+0 32-bit DirectClass 5.69KB 0.000u 0:00.000
app/static/favicon.ico[1] ICO 16x16 16x16+0+0 8-bit DirectClass 5.69KB 0.000u 0:00.000

Fixes #20149

Change-Id: I0feee344240d9900d1070e4d5c5423c0c6f155f9
Reviewed-on: https://go-review.googlesource.com/37591
Reviewed-by: Chris Broadfoot <cbro@golang.org>
diff --git a/app/static/favicon.ico b/app/static/favicon.ico
index d287722..8d22584 100644
--- a/app/static/favicon.ico
+++ b/app/static/favicon.ico
Binary files differ