add code coverage

.travis.yml

@@ -0,0 +1,13 @@
+language: python
+python:
+  - "3.6"
+# command to install dependencies
+install:
+  - pip install --quiet -r requirements.txt
+  - pip install pytest pytest-cov
+# command to run tests
+script:
+  - pytest --cov=./
+
+after_success:
+  - codecov

README.md

@@ -1,4 +1,6 @@
 # FastNLP
+[![Build Status](https://travis-ci.org/fastnlp/fastNLP.svg?branch=master)](https://travis-ci.org/fastnlp/fastNLP)
+[![codecov](https://codecov.io/gh/fastnlp/fastNLP/branch/master/graph/badge.svg)](https://codecov.io/gh/fastnlp/fastNLP)
 ```
 FastNLP
 ├── docs