Bump the version in setup.py

Author: mitmul

setup.py

@@ -7,7 +7,7 @@
         'onnx_chainer.functions',
         'onnx_chainer.testing',
     ],
-    version='1.3.0a2',
+    version='1.3.0a4',
     description='Convert a Chainer model into ONNX',
     long_description=open('README.md').read(),
     long_description_content_type='text/markdown',