Replace pil with Pillow in python package requirements

Debian package python-pil does install Pillow, the alive fork of dead
PIL project. When, however, pil is specified as package dependency in
setup.py, and python-ev3dev is installed with either
`easy_install python-ev3dev` or `python setup.py install`,
an attempt is made to install the actual PIL from PyPI. This fails on my
host system, and I think is not desired behavior anyway.

Also see ev3dev/ev3dev-lang#113

Author: ddemidov

setup.py

@@ -12,6 +12,6 @@
     url='https://github.com/rhempel/ev3dev-lang-python',
     include_package_data=True,
     py_modules=['ev3dev'],
-    install_requires=['pil']
+    install_requires=['Pillow']
     )