Fix the presubmitter

According to https://wiki.jenkins.io/display/JENKINS/Parameterized+Build
it should be enough to change our Get to a Post

Change-Id: I3a964e4214eee5e9979216a35a42fc1e0ddbbb78

jenkins/jenkins.go

diff --git a/jenkins/jenkins.go b/jenkins/jenkins.go
index f4d5a60..9f783e9 100644
--- a/jenkins/jenkins.go
+++ b/jenkins/jenkins.go
@@ -26,18 +26,13 @@
 
 // RunPresubmit queues a Jenkins presubmit build.
 func RunPresubmit(ref string) error {
-	url := (&url.URL{
-		Scheme: "http",
-		Host:   "localhost:8080",
-		Path:   "/job/gwt.presubmit/buildWithParameters",
-		RawQuery: url.Values{
-			"token":  {creds.JenkinsAuthToken()},
-			"COMMIT": {ref},
-		}.Encode(),
-	}).String()
+	data := url.Values{
+		"token":  {creds.JenkinsAuthToken()},
+		"COMMIT": {ref},
+	}
 
 	// TODO(mdempsky): Check for failed return codes?
-	resp, err := http.Get(url)
+	resp, err := http.PostForm("http://localhost:8080/job/gwt.presubmit/buildWithParameters", data)
 	if err == nil {
 		resp.Body.Close()
 	}