travis-ci: Update package list in before_install

[skip ci]

.travis.yml

@@ -1,7 +1,9 @@
 language: c
 
-install:
+before_install:
     - sudo apt-get update -qq
+
+install:
     - sudo apt-get install -qq --no-install-recommends perl autotools-dev libdbi-dev libldap2-dev libpq-dev libmysqlclient-dev libradiusclient-ng-dev libkrb5-dev libnet-snmp-perl procps mawk
     - sudo apt-get install -qq --no-install-recommends autoconf automake
     - tools/setup