use number of CPUs on machine for tests

.travis.yml

@@ -6,6 +6,6 @@ before_script:
 # for some tests  
   - sudo locale-gen de_DE && sudo locale-gen zh_CN.utf8
   - HPHP_HOME=`pwd` make -j 8
-script: hphp/hhvm/hhvm hphp/test/run --arg --threads 8 quick slow zend
+script: hphp/hhvm/hhvm hphp/test/run --arg quick slow zend
 notifications:
   irc: "chat.freenode.net#hhvm"