.travis.yml: add numpy and scipy packages

These two packages are used in wavetool.py,
pylint will complain if they are not installed.

Signed-off-by: Amery Song <chao.song@intel.com>

Author: Amery Song

.travis.yml

@@ -16,7 +16,7 @@ git:
   quiet: true
 
 before_install:
-  - sudo apt-get -y install shellcheck pylint
+  - sudo apt-get -y install shellcheck pylint python3-numpy python3-scipy
 
 jobs:
   include: