Use zef instead of panda

Author: titsuki

.travis.yml

@@ -5,9 +5,9 @@ language: perl6
 perl6:
   - latest
 install:
-  - rakudobrew build-panda
-  - panda --notests installdeps .
+  - rakudobrew build-zef
+  - zef --debug --depsonly --/test install .
 script:
-  - perl6 -MPanda::Builder -e 'Panda::Builder.build(~$*CWD)'
+  - zef build .
   - PERL6LIB=$PWD/lib prove -e perl6 -vr t/
 sudo: false