Use new wheels site and do not install tifffile until optional

.travis.yml

@@ -17,7 +17,7 @@ python:
 before_install:
     - export DISPLAY=:99.0
     - export PYTHONWARNINGS="all"
-    - export WHEELHOUSE="--no-index --find-links=http://wheels.scikit-image.org/"
+    - export WHEELHOUSE="--no-index --find-links=http://travis-wheels.scikit-image.org/"
     - travis_retry tools/travis_setup.sh
 
 install:

tools/travis_install_optional.sh

@@ -30,3 +30,5 @@ pip install astropy
 if [[ $TRAVIS_PYTHON_VERSION == 2.* ]]; then
     pip install pyamg
 fi
+
+pip install tifffile

tools/travis_setup.sh

@@ -15,8 +15,6 @@ if [[ $TRAVIS_PYTHON_VERSION == 2.7* ]]; then
     pip install https://github.com/networkx/networkx/archive/networkx-1.8.tar.gz
 fi
 
-pip install $WHEELHOUSE numpy
-pip install tifffile
 pip install -r requirements.txt $WHEELHOUSE
 python check_bento_build.py