Override prettyPrint's colour choice (red) for strings in quotes.

I've moved the docs.css to last so it can tweak any existing css, and
then set that to the same grey colour used for 'normal' text.

While testing I found and fixed an over-zealous line wrap.

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@docker.com> (github: SvenDowideit)

docs/theme/mkdocs/css/docs.css

@@ -335,3 +335,7 @@ table.table tr td img {
 #versionnav ul ul {
     padding: 0;
 }
+
+/* over-ride the prettyPrint colouring */
+
+.str, .atv { color: #48484C; }