Revert "Update git plugin and its dependencies"

This reverts commit 6df841026fc4c4ae361e6a4b01e670a14b74eebc.

Reason for revert: Broke gerrit-ci.googlesource.com because
of Matrix Project Plugin version 1.13 is older than required.

Change-Id: I9452fc37da426076f46d60e72deecd9375139ff5
diff --git a/jenkins-docker/master/plugins.txt b/jenkins-docker/master/plugins.txt
index bf16538..b05dac8 100644
--- a/jenkins-docker/master/plugins.txt
+++ b/jenkins-docker/master/plugins.txt
@@ -37,7 +37,7 @@
 gatling:1.2.5
 gatling-check:1.0.0
 gerrit-code-review:0.4.0
-git:4.0.0
+git:3.9.1
 git-client:3.0.0
 github:1.29.5
 github-api:1.92
@@ -55,7 +55,7 @@
 icon-shim:2.0.3
 jquery-detached:1.2.1
 junit:1.24
-mailer:1.29
+mailer:1.21
 mask-passwords:2.12.0
 matrix-auth:2.2
 matrix-project:1.13