add coveralls support to travis config

based on instructions at
https://coveralls.zendesk.com/hc/en-us/articles/201342809-Go

also remove drone.io badge from README.md, since it looks like the
service is no more.

Fixes #694

.travis.yml

@@ -8,12 +8,18 @@ matrix:
   allow_failures:
     - go: master
   fast_finish: true
+env:
+  secure: "IrnPmy/rkIP6Nrbqji+u7MCAibQlA6WvPLEllmDQ2yZP/uIe3wLwwYbTu9BOkgzoLA+f8PA6u3pp/RhY/rtaM4NzHAO2nVfGIv9UHUQ3NGq0DYS6rODjVKhq7vkhELoagRewyqFVN4rE0LnExkknRMgjQfRke6/DA7u7Xm8JyhY=" # COVERALLS_TOKEN
 install:
-  - # Do nothing. This is needed to prevent default install action "go get -t -v ./..." from happening here (we want it to happen inside script step).
+  - go get golang.org/x/tools/cmd/cover
+  - go get github.com/mattn/goveralls
+  - # Do not install go-github yet, since we want it to happen inside the script step.
 script:
   - go get -t -v ./...
   - diff -u <(echo -n) <(gofmt -d -s .)
   - go generate -x ./... && git diff --exit-code; code=$?; git checkout -- .; (exit $code) # Check that go generate ./... produces a zero diff; clean up any changes afterwards.
   - go tool vet .
   - go test -v -race ./...
   - go test -v -tags=integration -run=^$ ./test/integration # Check that integration test builds successfully, but don't run any of the tests (they hit live GitHub API).
+  - go test -v -covermode=count -coverprofile=coverage.out ./github
+  - $HOME/gopath/bin/goveralls -coverprofile=coverage.out -service=travis-ci -repotoken $COVERALLS_TOKEN

README.md

@@ -5,7 +5,7 @@ go-github is a Go client library for accessing the [GitHub API][].
 **Documentation:** [![GoDoc](https://godoc.org/github.com/google/go-github/github?status.svg)](https://godoc.org/github.com/google/go-github/github)  
 **Mailing List:** [go-github@googlegroups.com](https://groups.google.com/group/go-github)  
 **Build Status:** [![Build Status](https://travis-ci.org/google/go-github.svg?branch=master)](https://travis-ci.org/google/go-github)  
-**Test Coverage:** [![Test Coverage](https://coveralls.io/repos/google/go-github/badge.svg?branch=master)](https://coveralls.io/r/google/go-github?branch=master) ([gocov report](https://drone.io/github.com/google/go-github/files/coverage.html))
+**Test Coverage:** [![Test Coverage](https://coveralls.io/repos/google/go-github/badge.svg?branch=master)](https://coveralls.io/r/google/go-github?branch=master)
 
 go-github requires Go version 1.7 or greater.