content/static: fix spacing between links in right sidebar
content/static: fix spacing between links in right sidebar

Screenshot: https://photos.app.goo.gl/djZcwfA8mDtRGQzy7

Change-Id: I5b62d37b4a62da6b10958746ff1bee9eff4cd806
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/275876
Reviewed-by: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
Trust: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>
Trust: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Run-TryBot: Julie Qiu <8d32267b6b4884cf35adeaccde2b6857ae11aace@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite