Convert scripts into entry_points

The recommended approach to create launch scripts is to use entry_points
and console_scripts.

xref: https://packaging.python.org/guides/distributing-packages-using-setuptools/#scripts

setup.py

@@ -53,7 +53,11 @@ setup(
                       'boto3',
                       'requests',
                       'tqdm'],
-    scripts=["bin/pytorch_pretrained_bert"],
+    entry_points={
+      'console_scripts': [
+        "pytorch_pretrained_bert=pytorch_pretrained_bert.__main__:main"
+      ]
+    },
     python_requires='>=3.5.0',
     tests_require=['pytest'],
     classifiers=[