only ask for coverage when it works (not js)

.travis.yml

@@ -1,45 +1,46 b''
 # http://travis-ci.org/#!/ipython/ipython
 language: python
 python:
     - 3.4
     - 2.7
     - 3.3
 env:
     - GROUP=js/base
     - GROUP=js/notebook
     - GROUP=js/services
     - GROUP=js/tree
     - GROUP=js/widgets
     - GROUP=
 before_install:
     # workaround for https://github.com/travis-ci/travis-cookbooks/issues/155
     - sudo rm -rf /dev/shm && sudo ln -s /run/shm /dev/shm
     # Pierre Carrier's PPA for PhantomJS and CasperJS
     - sudo add-apt-repository -y ppa:pcarrier/ppa
     # Needed to get recent version of pandoc in ubntu 12.04
     - sudo add-apt-repository -y ppa:marutter/c2d4u
     - sudo apt-get update
     - sudo apt-get install pandoc casperjs libzmq3-dev
     - git clone --quiet --depth 1 https://github.com/minrk/travis-wheels travis-wheels
     - 'if [[ $GROUP == js* ]]; then python -m IPython.external.mathjax; fi'
+    - 'if [[ $GROUP != js* ]]; then COVERAGE="--coverage xml"; fi'
 install:
     - pip install coveralls
     - pip install -f travis-wheels/wheelhouse file://$PWD#egg=ipython[all]
 script:
-    - cd /tmp && iptest $GROUP --coverage xml && cd -
+    - cd /tmp && iptest $GROUP $COVERAGE && cd -
 
 matrix:
     exclude:
         - python: 3.3
           env: GROUP=js/base
         - python: 3.3
           env: GROUP=js/notebook
         - python: 3.3
           env: GROUP=js/tree
         - python: 3.3
           env: GROUP=js/widgets
 
 after_success:
     - cp /tmp/ipy_coverage.xml ./
     - cp /tmp/.coverage ./
     - coveralls