Send messages to topics for android

[appleboy]

fix #265

Using binary:

$ gorush --android --topic "/topics/foo-bar" -m "This is a Firebase Cloud Messaging Topic Message" -k xxxxxxxxxx

Send JSON file:

$ bat POST localhost:8088/api/push notifications:=@test.json

result:

POST /api/push HTTP/1.1
Host: localhost:8088
Accept: application/json
Accept-Encoding: gzip, deflate
Content-Type: application/json
User-Agent: bat/0.1.0


{"notifications":[{"message":"This is a Firebase Cloud Messaging Topic Message","platform":2,"to":"/topics/foo-bar"}]}


HTTP/1.1 200 OK
Content-Type : application/json; charset=utf-8
X-Drone-Version : v1.9.0-84-g098f9da
Date : Tue, 24 Oct 2017 08:42:56 GMT
Content-Length : 242


{
  "counts": 1,
  "logs": [],
  "success": "ok"
}

Data:

{
  "notifications": [{
    "message": "This is a Firebase Cloud Messaging Topic Message",
    "platform": 2,
    "to": "/topics/foo-bar"
  }]
}

Server Log:

[codecov-io]

Codecov Report

Merging #296 into master will increase coverage by 0.16%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #296      +/-   ##
==========================================
+ Coverage   92.78%   92.95%   +0.16%     
==========================================
  Files          16       16              
  Lines        1247     1277      +30     
==========================================
+ Hits         1157     1187      +30     
  Misses         68       68              
  Partials       22       22

Impacted Files	Coverage Δ
gorush/notification_fcm.go	89.39% <100%> (+2.12%)	⬆️
gorush/notification.go	100% <100%> (ø)	⬆️
gorush/worker.go	100% <100%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 4df2420...098f9da. Read the comment docs.