travis: Build using the daily PPA

Now that we depend on seccomp2, the backport currently in precise is too
old to allow for a succesful build, so instead use ppa:ubuntu-lxc/daily
which contains recent versions of all needed build-dependencies.

Signed-off-by: Stéphane Graber <stgraber@ubuntu.com>

.travis.yml

@@ -3,6 +3,7 @@ compiler:
  - gcc
  - clang
 before_install:
+ - sudo add-apt-repository ppa:ubuntu-lxc/daily -y
  - sudo apt-get update -qq
  - sudo apt-get install -qq libapparmor-dev libcap-dev libseccomp-dev python3-dev docbook2x libgnutls-dev liblua5.2-dev libselinux1-dev
 script: ./autogen.sh && ./configure --enable-tests && make -j4