Use -e flag to install on Travis

.travis.yml

@@ -1,38 +1,38 b''
 # http://travis-ci.org/#!/ipython/ipython
 language: python
 python:
     - 3.4
     - 2.7
 sudo: false
 env:
   global:
     - PATH=$TRAVIS_BUILD_DIR/pandoc:$PATH
   matrix:
     - GROUP=
     - GROUP=js/base
     - GROUP=js/notebook
     - GROUP=js/services
     - GROUP=js/tree
     - GROUP=js/widgets
 before_install:
     - 'if [[ $GROUP != js* ]]; then wget https://7de4dfdec62155b49b44-d726a73613a1989d29b147f20996e7c1.ssl.cf2.rackcdn.com/pandoc-1.12.3-linux-debian-x86_64.zip && unzip pandoc-1.12.3-linux-debian-x86_64.zip; fi'
     - 'if [[ $GROUP == js* ]]; then wget https://7de4dfdec62155b49b44-d726a73613a1989d29b147f20996e7c1.ssl.cf2.rackcdn.com/mathjax.zip; fi'
     - 'if [[ $GROUP == js* ]]; then npm install -g casperjs; fi'
     - git clone --quiet --depth 1 https://github.com/minrk/travis-wheels travis-wheels
     - 'if [[ $GROUP != js* ]]; then COVERAGE="--coverage xml"; fi'
 install:
-    - pip install -f travis-wheels/wheelhouse file://$PWD#egg=ipython[all] coveralls
+    - pip install -f travis-wheels/wheelhouse -e file://$PWD#egg=ipython[all] coveralls
 before_script:
     - 'if [[ $GROUP == js* ]]; then python -m IPython.external.mathjax mathjax.zip; fi'
 script:
     - cd /tmp && iptest $GROUP $COVERAGE && cd -
 
 matrix:
     include:
         - python: 3.3
           env: GROUP=
 
 after_success:
     - cp /tmp/ipy_coverage.xml ./
     - cp /tmp/.coverage ./
     - coveralls