number: fix typo
number: fix typo

Change-Id: Iee2b9cd52e9bc147ae595cb4d50f5096afaa3492
GitHub-Last-Rev: 922e349cdc4378ba52a15b395bf614b71246a7a3
GitHub-Pull-Request: golang/text#14
Reviewed-on: https://go-review.googlesource.com/c/text/+/231121
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/text