Elimino instalación de paquete en builds de travis

.travis.yml

@@ -15,7 +15,7 @@ before_install:
 - docker info
 - sudo apt-get remove docker docker-engine
 - sudo apt-get update
-- sudo apt-get install linux-image-extra-$(uname -r) linux-image-extra-virtual apt-transport-https ca-certificates curl software-properties-common npm
+- sudo apt-get install linux-image-extra-virtual apt-transport-https ca-certificates curl software-properties-common npm
 - curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
 - sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
 - sudo apt-get update