Fix build guide when returning to normal

This fixes a small error in the build guide. Instead of `--catalog`, `--lookup`
should be used to return to the default installation of a package.

Author: jryans

build.md

@@ -807,7 +807,7 @@ Some information that might improve your experience:
 * If you’re done and want to go back to the normal installation for
   <_pkg-name_>, use
 
-    `raco pkg update --catalog <pkg-name>`
+    `raco pkg update --lookup <pkg-name>`
 
 * See Developing Packages with Git for more information about how
   packages are meant to work as Git repositories.

pkgs/racket-build-guide/contribute.scrbl

@@ -140,7 +140,7 @@ Some information that might improve your experience:
  @item{If you're done and want to go back to the normal installation
        for @nonterm{pkg-name}, use
 
-        @commandline{raco pkg update @DFlag{catalog} @nonterm{pkg-name}}}
+        @commandline{raco pkg update @DFlag{lookup} @nonterm{pkg-name}}}
 
  @item{See @secref["git-workflow" #:doc '(lib
        "pkg/scribblings/pkg.scrbl")] for more information about how