Travis-CI: clean away cruf in definition file and use correct syntax

.travis.yml

@@ -8,13 +8,9 @@ dist: trusty
 language: cpp
 compiler:
   - gcc
-#  - clang # See commit f38808 if you want to re-enable clang builds
 cache:
-  apt:
-  ccache:
-
-# Timing on build an test needs to be < 50 minutes. The compile is ~4-5minutes
-# so here we group the tests such that this happens.
+  - apt
+  - ccache
 
 addons:
   apt:
@@ -37,7 +33,7 @@ addons:
       - po-debconf
       - psmisc
       - zlib1g-dev
-      - libcrack2-dev # no effect as the package is disallowed on Travis-CI
+      - libcrack2-dev
       - libjemalloc-dev
       - devscripts # implicit for any build on Ubuntu