test: use lower-case error message in heapsampling.go
According to Go style guidelines, error strings should not be capitalized.
Change-Id: Iacfb3f5192b7be40da99b6b7e4801f1ae1169efc
GitHub-Last-Rev:
440396e0946edb18c422442ea235b5c57c2899af
GitHub-Pull-Request: golang/go#76999
Reviewed-on: https://go-review.googlesource.com/c/go/+/732760
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>