Add codecov CI config

Signed-off-by: Eric Zhao <[email protected]>

Author: sczyh30

Diff for: .codecov.yml

@@ -0,0 +1,2 @@
+ignore:
+  - "example/.*"

Diff for: .travis.yml

@@ -9,5 +9,9 @@ go:
   - 1.14.x
 env:
   - GO111MODULE=on
+
 script:
-  - go test -v -race ./...
+  - go test -v -race ./... -coverprofile=coverage.txt -covermode=atomic
+
+after_success:
+  - bash <(curl -s https://codecov.io/bash)