changed classifiers for v1.0 in setup.py

pypiのDevelopment Status :: 4 - Betaになっていますが、もはやベータではないと思うので、Production/Stableへ変更すべきと思います。

```
diff --git a/setup.py b/setup.py
index 2ae1cae..690ec76 100644
--- a/setup.py
+++ b/setup.py
@@ -31,7 +31,7 @@ setup(
     cmdclass={'test': PyTest},
     long_description=long_description,
     classifiers=[
-        'Development Status :: 4 - Beta',
+        'Development Status :: 5 - Production/Stable'
         'Operating System :: OS Independent',
         'License :: OSI Approved :: MIT License',
         'Intended Audience :: Developers',
```