text.Doc: trim space
text.Doc: trim space

Trim all leading and trailing whitespace. This makes flag usage
more consise.

Change-Id: If95201d219bfee9b00eb57d6fb003747fe710054
Reviewed-on: https://chromium-review.googlesource.com/c/infra/luci/luci-go/+/1949059
Reviewed-by: Yuke Liao <ae0d415ded8b6ec8d2a31886de00254b719d927e@chromium.org>
Reviewed-by: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>
Commit-Queue: Nodir Turakulov <ef4933a197ef7b4b3f55f1bec4942aead3637a2a@chromium.org>

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