Adding missing comma to first example

The first example script in the instructions does not work.
The error {"error":"Failed to parse body as JSON"} is returned from curl.
There is a missing comma in the JSON expression.

Author: rptb1

user/triggering-builds.md

@@ -23,7 +23,7 @@ Trigger Travis CI builds using the API V3 by sending a POST request to `/repo/{s
    ```bash
    body='{
    "request": {
-   "branch":"master"
+   "branch":"master",
    "sha":"bf944c952724dd2f00ff0c466a5e217d10f73bea"
    }}'