html/template: fix typo in content_test.go

html/template: fix typo in content_test.go

esacped -> escaped

Change-Id: I253c46b30bb1cf7cdfb4668628907d16428fefb9
GitHub-Last-Rev: accd0e089f35b93c7e26725fcac5c048799db022
GitHub-Pull-Request: golang/go#53553
Reviewed-on: https://go-review.googlesource.com/c/go/+/414274
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Ian Lance Taylor <iant@google.com>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Ian Lance Taylor <iant@google.com>