[isolated] Use github.com/klauspost/compress/zlib for compression
[isolated] Use github.com/klauspost/compress/zlib for compression

'compress/zlib' in go1.15 had a regression, see https://github.com/golang/go/issues/41420. As a temporary workaround, we switch to this zlib module.

I tested this change locally by uploading the corrupted data via `isolate`. This time the verification passed:

* Uploaded isolated: https://isolateserver-dev.appspot.com/browse?namespace=default-gzip&digest=d6ec4c1007fe17bab16278cded13bffff0999932
* Digest for content_browsertests: a6dfa48b2f14b199b99a9eed601609a00fb072a1

Bug: 1128181
Change-Id: I376c5278cb5e4503a0f2adb4935d84262401d09b
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/2413814
Commit-Queue: Ye Kuang <1cd89f22f3967fc3dcb883b53940be4b98ec483f@google.com>
Commit-Queue: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>
Auto-Submit: Ye Kuang <1cd89f22f3967fc3dcb883b53940be4b98ec483f@google.com>
Reviewed-by: Junji Watanabe <aaef61ef98ffea505db831f310be2a0eb8492537@google.com>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go