Adds gfortran to Travis CI env so that it's available to numpy.

Also drops ipython (which is used for desktop development) and
nose (which is installed by default by Travis CI) from list of
dev packages to be installed during a Travis build.

.travis.yml

@@ -2,7 +2,8 @@ language: python
 python:
   - "2.7"
 install:
-  - pip install -r etc/requirements_dev.txt
+  - apt-get install gfortran
+  - cat etc/requirements_dev.txt  | grep -v "^#" | grep -v "^$" | grep -v ipython | grep -v nose | xargs pip install
   - etc/ordered_pip.sh etc/requirements.txt
 before_script:
   - "flake8 zipline tests"