Add Coveralls integration

.travis.yml

@@ -17,6 +17,7 @@ before_install:
   - sudo add-apt-repository ppa:jonathonf/ffmpeg-4 -y
   - sudo apt-get update -q
   - sudo apt-get install libavcodec-dev libavdevice-dev libavfilter-dev libavformat-dev libavresample-dev libavutil-dev libpostproc-dev libswresample-dev libswscale-dev -y
+  - go get -u github.com/mattn/goveralls
 
 install:
   - go get -u golang.org/x/lint/golint
@@ -31,3 +32,6 @@ script:
   - diff -u <(echo -n) <(go vet ./)
   - diff -u <(echo -n) <(golint ./)
   - go test -v -race -covermode=atomic -coverprofile=coverage.out
+
+after_success:
+  - goveralls -coverprofile=coverage.out -service=travis-ci