add ansi colors to new jenkins builds

Change-Id: Ifc0f581522afa596b23e7a839dbea7abc9865b79
Reviewed-on: https://gerrit.instructure.com/182145
Reviewed-by: Robert Lamb <rlamb@instructure.com>
QA-Review: Robert Lamb <rlamb@instructure.com>
Product-Review: Robert Lamb <rlamb@instructure.com>
Tested-by: Jenkins

Jenkinsfile

@@ -3,6 +3,10 @@
 pipeline {
     agent { label 'docker' }
 
+    options {
+      ansiColor('xterm')
+    }
+
     environment {
         NAME = "${env.GERRIT_REFSPEC}".minus('refs/changes/').replaceAll('/','.')
         IMAGE_TAG = "$DOCKER_REGISTRY_FQDN/canvas-lms:$NAME"