Require tensorflow 1.4.1 (#315)

* Require tensorflow 1.4.1

* modified the python/README.md

python/README.md

 * numpy
 * Pillow
 * Python (2 or 3)
-* Tensorflow (1.0+)
+* Tensorflow (1.4)
 
 ### Installing Dependencies
 To install dependencies, run:

python/requirements.txt

-tensorflow>=1.0
+tensorflow==1.4.1
 Pillow>=4.2.1
 matplotlib
 numpy>=1.11.0