travis-ci: Remove gawk to build against mawk

.travis.yml

@@ -2,6 +2,7 @@ language: c
 
 before_install:
   - sudo apt-get update -qq
+  - sudo apt-get purge -qq gawk
 
 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