python3 shebang from #620 (#621)

* python3 shebang from #620
* Add changelog entry for python3 change

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
   absolute and not relative. We assumed incorrectly that epsilon is absolute tolerance.
 
 ### Changed
+- Python scripts start with #!/usr/bin/env python3 instead of python
 - Changed compile flags -Ofast to -O3 and remove --ffinite-math
 - Moved old graph groups to depracated folder
 - Make cublas and cusparse handle inits lazy to save memory when unused

scripts/checkpoints/average.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 """
 This script takes multiple Marian *.npz model files and outputs an elementwise average of the model,
 meant to do check-point averaging from: 

scripts/contrib/inject_ctt.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 from __future__ import print_function
 

scripts/contrib/inject_model_params.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 from __future__ import print_function
 

scripts/embeddings/prepare_corpus.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 from __future__ import print_function

scripts/embeddings/process_word2vec.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 # -*- coding: utf-8 -*-
 
 from __future__ import print_function

scripts/server/client_example.py

@@ -1,4 +1,4 @@
-#!/usr/bin/env python
+#!/usr/bin/env python3
 
 from __future__ import print_function, unicode_literals, division