use parallel make

Author: guoxiao

.travis.yml

@@ -2,10 +2,10 @@ language: perl
 perl:
 - '5.16'
 - '5.14'
-install: 
+install:
 - sudo apt-get update -qq
 - sudo apt-get install -y openssl libcppunit-dev libreadline6 libreadline6-dev valgrind realpath libmodule-install-perl
-script: "make && make test-fast && make perl"
+script: "make -j2 && make test-fast && make perl"
 notifications:
   irc:
     - "irc.freenode.net#mdbm"