added matplotlib to the requirements

.travis.yml

@@ -4,7 +4,7 @@ python:
 virtualenv:
   system_site_packages: true
 before_install:
-  - sudo apt-get install -qq python-numpy python-scipy
+  - sudo apt-get install -qq python-numpy python-scipy python-matplotlib
 # command to install dependencies
 install: "pip install -r requirements.txt --use-mirrors"
 # command to run tests

requirements.txt

@@ -1,3 +1,4 @@
 numpy
 scipy
 ipython
+matplotlib