Fix #33

[momijiame]

This patch will switch to use __future__.print_function.
By this, It will be able to use print() function at Python 2.x and 3.x as well.

$ python
Python 3.6.3 (default, Oct 10 2017, 01:16:10) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.37)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from eralchemy import helpers
>>> helpers.fail('test')
Error: test

$ python 
Python 3.6.3 (default, Oct 10 2017, 01:16:10) 
[GCC 4.2.1 Compatible Apple LLVM 9.0.0 (clang-900.0.37)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from script import make_release
>>> make_release.info('test')
Error: test
>>> make_release.fail('test')
Error: test

$ python
Python 2.7.10 (default, Feb  7 2017, 00:08:15) 
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.34)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> from eralchemy import helpers
>>> helpers.fail('test')
Error: test

$ python
Python 2.7.10 (default, Feb  7 2017, 00:08:15) 
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.34)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> 
>>> from script import make_release
>>> make_release.info('test')
Error: test
>>> make_release.fail('test')
Error: test