.travis.yml: add libaio-dev

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

.travis.yml

@@ -6,6 +6,6 @@ compiler:
   - gcc
 before_install:
   - sudo apt-get update -qq
-  - sudo apt-get install -qq protobuf-c-compiler libprotobuf-c0-dev
+  - sudo apt-get install -qq protobuf-c-compiler libprotobuf-c0-dev libaio-dev
 script:
   - "bash -ex scripts/travis-ci.sh"