use wxpython wheel

.travis.yml

@@ -45,6 +45,9 @@ install:
 - sudo apt-get update
 - sudo apt-get install inkscape
 
+# wxPython doen't publish linux wheels in pypi
+- pip install http://extras.wxpython.org/wxPython4/extras/linux/gtk3/ubuntu-14.04/wxPython-4.0.0b2-cp27-cp27mu-linux_x86_64.whl
+
 # We can't use the shapely wheel because it includes the geos
 # library but with a weird file name.  Details:
 # https://github.com/pyinstaller/pyinstaller/blob/61b1c75c2b0469b32d114298a63bf60b8d597e37/PyInstaller/hooks/hook-shapely.py#L34