Update README.md
Fix typo.
@@ -27,8 +27,8 @@ python setup.py install
```bash
docker build -f docker/alpine.df . -t pycat:alpine
docker build -f docker/centos7.df . -t pycat:centos7
-docker build -f docker/ubuntu1404.df . -t pycat:ubuntu18.04
-docker build -f docker/ubuntu1604.df . -t pycat:ubuntu18.04
+docker build -f docker/ubuntu1404.df . -t pycat:ubuntu14.04
+docker build -f docker/ubuntu1604.df . -t pycat:ubuntu16.04
docker build -f docker/ubuntu1804.df . -t pycat:ubuntu18.04
```
