Merge pull request #2068 from edx/zoldak/git-install-on-jenkins-workers

Update the source list after adding git ppa TE-907

util/packer/jenkins_worker.json

@@ -44,6 +44,9 @@
     "inline": ["sudo add-apt-repository ppa:git-core/ppa -y"]
   }, {
     "type": "shell",
+    "inline": ["sudo apt-get update"]
+  }, {
+    "type": "shell",
     "inline": ["sudo apt-get -y install git-core"]
   }, {
     "type": "shell",