freebsd.sh: install py38-pip

Signed-off-by: Arthur She <arthur.she@linaro.org>
Change-Id: I68ee41303af1c4139bbd553caa60ad889bf12795
diff --git a/freebsd.sh b/freebsd.sh
index a40fdcc..d4fd3ae 100644
--- a/freebsd.sh
+++ b/freebsd.sh
@@ -17,7 +17,7 @@
     gmake \
     perl5 \
     bash \
-    py36-pip
+    py38-pip
 
 mount -t fdescfs fdesc /dev/fd
 mount -t procfs proc /proc