Use correct syntax markup for shell

Approved by:	carlavilla

documentation/content/en/books/fdp-primer/overview/chapter.adoc

@@ -44,21 +44,21 @@ Some preparatory steps must be taken before editing the FreeBSD documentation. F
 ====
 . Install these packages. These packages are all of the software needed to edit and build FreeBSD documentation. The Git package is needed to obtain a working copy of the documentation and generate patches with.
 +
-[source,bash]
+[source,shell]
 ....
 # pkg install gohugo python3 git-lite rubygem-asciidoctor rubygem-rouge
 ....
 +
 . Optional: to generate PDF documentation install `asciidoctor-pdf`
 +
-[source,bash]
+[source,shell]
 ....
 # pkg install rubygem-asciidoctor-pdf 
 ....
 +
 . Install a local working copy of the documentation from the FreeBSD repository in [.filename]#~/doc# (see <<working-copy>>).
 +
-[source,bash]
+[source,shell]
 ....
 % git clone https://git.FreeBSD.org/doc.git doc
 ....
@@ -76,14 +76,14 @@ Review the output and edit the file to fix any problems shown, then rerun the co
 +
 . _Always_ build-test changes before submitting them. Running `make` in the top-level directory of the documentation will generate that documentation in HTML format.
 +
-[source,bash]
+[source,shell]
 ....
 make
 ....
 +
 . When changes are complete and tested, generate a "diff file":
 +
-[source,bash]
+[source,shell]
 ....
 % cd ~/doc
 % git diff > bsdinstall.diff.txt