Travis-CI: install new autoconf-archive build-dependency

Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
[smcv: cherry-picked from master to dbus-1.10 to get the Travis-CI setup
consistent between the two branches; it is not strictly needed on dbus-1.10]

.travis.yml

@@ -12,6 +12,7 @@ install:
   - sudo apt-get -qq -y build-dep dbus
   - >
     sudo apt-get -qq -y install
+    autoconf-archive
     automake
     autotools-dev
     debhelper