Pin envinject-api plugin version

The newest version of the envinject-api plugin was not compatible with
Jenkins 2.60.3.

Change-Id: Ib763f8f52b5af1f4a7f454db4bbab0cf053bad77
diff --git a/jenkins-docker/master/plugins.txt b/jenkins-docker/master/plugins.txt
index a0574a2..f9e2952 100644
--- a/jenkins-docker/master/plugins.txt
+++ b/jenkins-docker/master/plugins.txt
@@ -33,6 +33,7 @@
 durable-task:1.22
 embeddable-build-status:1.9
 envinject:2.1.5
+envinject-api:1.5
 git:3.9.1
 git-client:2.7.2
 github:1.29.1