encoding/base64: fix typo in decodeQuantum docs
encoding/base64: fix typo in decodeQuantum docs

Change-Id: I643540bcea574d8a70b79237d97097dcc7368766
GitHub-Last-Rev: e2be58d1ab84f91dfbba1067aae7145f24fd650d
GitHub-Pull-Request: golang/go#28125
Reviewed-on: https://go-review.googlesource.com/c/141119
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

CAFxX/go,nawawi/go,nawawi/go,nawawi/go,akutz/go,cloudflare/go,josharian/go,akutz/go,cloudflare/go,golang/go,cloudflare/go,akutz/go,nawawi/go,cloudflare/go,golang/go,josharian/go,CAFxX/go,golang/go,josharian/go,CAFxX/go,golang/go,CAFxX/go,akutz/go,cloudflare/go,golang/go,cloudflare/go,golang/go,josharian/go,golang/go,josharian/go,golang/go,akutz/go,CAFxX/go,akutz/go,CAFxX/go,nawawi/go,nawawi/go,nawawi/go,josharian/go,CAFxX/go,CAFxX/go,akutz/go,cloudflare/go,josharian/go,cloudflare/go,akutz/go,josharian/go,nawawi/go