Fix casing to make weston auto start at boot.

systemd[1]: /lib/systemd/system/weston.service:26: Unknown section 'install'. Ignoring.

Change-Id: Ic753d2eec2efd9db23cf27d517476c40e0ba0332
diff --git a/debian/lib/systemd/system/weston.service b/debian/lib/systemd/system/weston.service
index 2886efe..7327a26 100644
--- a/debian/lib/systemd/system/weston.service
+++ b/debian/lib/systemd/system/weston.service
@@ -56,5 +56,5 @@
 UtmpIdentifier=tty7
 UtmpMode=user
 
-[install]
+[Install]
 WantedBy=graphical.target