Various fixes to the 13.0 installation doc.

- Remove spurious quotes around the release name and number.

- Replace SVN with Git.

- Fix a freebsd-update example to expand the localRel attribute.

Reviewed by:	gjb
Differential Revision:	https://reviews.freebsd.org/D29242

website/content/en/releases/13.0R/installation.adoc

@@ -3,8 +3,8 @@ title: "FreeBSD 13.0-RELEASE Installation Instructions"
 sidenav: download
 ---
 
-:releaseCurrent: "13.0-RELEASE"
-:localRel: "13.0"
+:releaseCurrent: 13.0-RELEASE
+:localRel: 13.0
 
 = FreeBSD {localRel}-RELEASE Installation Instructions
 
@@ -34,7 +34,7 @@ If you are upgrading from a previous release of FreeBSD, please read upgrading s
 
 The procedure for doing a source code based update is described in Updating FreeBSD from Source.
 
-For SVN use the releng/{localRel} branch which will be where any upcoming Security Advisories or Errata Notices will be applied.
+For Git use the releng/{localRel} branch which will be where any upcoming Security Advisories or Errata Notices will be applied.
 
 [[upgrade-binary]]
 == Upgrading Using "FreeBSD Update"
@@ -49,7 +49,7 @@ The {{< manpage "freebsd-update" "8">}} utility supports binary upgrades of i386
 
 Now the {{< manpage "freebsd-update" "8">}} utility can fetch bits belonging to {releaseCurrent}. During this process {{< manpage "freebsd-update" "8">}} will ask for help in merging configuration files.
 
-[.screen]
+[.screen,subs="verbatim,attributes"]
 ----
 # freebsd-update upgrade -r {localRel}-RELEASE
 # freebsd-update install