net/http: change TimeoutHandler's docs to match its new interfaces
net/http: change TimeoutHandler's docs to match its new interfaces

As of Go 1.13rc1, TimeoutHandler supports the Flusher and Pusher interfaces and
this change corrects its documentation to say that.

Fixes #33769
Updates #29193

Change-Id: Ia0523f7f2e3dc1f8f0b68950b85a7bf81c4abe60
GitHub-Last-Rev: 5310d2c9608a1af2d3030a9573e920906c76744e
GitHub-Pull-Request: golang/go#33770
Reviewed-on: https://go-review.googlesource.com/c/go/+/191237
Reviewed-by: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
Run-TryBot: Andrew Bonventre <682ad9f487f614f19e8b7cc5d340bdc8e1c1b128@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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