add Codecov

.travis.yml

@@ -22,4 +22,9 @@ before_install:
 
 script:
   - go get -t ./...
-  - ginkgo -r --randomizeAllSpecs --randomizeSuites --trace --progress
+  - ginkgo -r --cover --randomizeAllSpecs --randomizeSuites --trace --progress
+
+after_success:
+  - cat libp2p-quic-transport.coverprofile > coverage.txt
+  - cat */*.coverprofile >> coverage.txt
+  - bash <(curl -s https://codecov.io/bash) -f coverage.txt

codecov.yml

+coverage:
+  round: nearest
+  status:
+    project:
+      default:
+        threshold: 0.5
+    patch: false