Add tempita to python packages.

sel4-sys uses tempita in constructing rust system call wrappers.

Change-Id: I662cc96af00a4cd8775d2a3f59e128f9b9079326

install-prereqs.sh

diff --git a/install-prereqs.sh b/install-prereqs.sh
index 6da5bb5..14d8e17 100755
--- a/install-prereqs.sh
+++ b/install-prereqs.sh
@@ -97,6 +97,7 @@
     mako
     matplotlib
     requests
+    tempita
     wget
 )