Merge pull request PowerDNS#6142 from Habbie/auth-4.1.x-travis

auth 4.1.x: limit travis builds to auth only

.travis.yml

@@ -6,19 +6,6 @@ compiler:
   - clang
 env:
   - PDNS_BUILD_PRODUCT=auth
-  - PDNS_BUILD_PRODUCT=recursor
-  - PDNS_BUILD_PRODUCT=dnsdist
-
-matrix:
-  exclude:
-    - compiler: clang
-      env: PDNS_BUILD_PRODUCT=recursor
-  include:
-    - compiler: clang
-      env: PDNS_BUILD_PRODUCT=recursor COMPILER=clang++-3.6
-      addons:
-        apt:
-          packages: ['clang-3.6']
 
 before_script:
   - git describe --always --dirty=+