Travis: Install missing -lcares library

Author: jonnor

.travis.yml

@@ -10,6 +10,7 @@ before_install:
 - sudo apt-get update -qq
 - sudo apt-get install g++-4.8
 - sudo apt-get install libboost1.55-all-dev
+- sudo apt-get install pkg-config cmake openssl libc-ares-dev
 install:
 - wget http://mosquitto.org/files/source/mosquitto-1.3.1.tar.gz
 - tar xzf mosquitto-1.3.1.tar.gz