Update Git version for source installs to match Omnibus

.gitlab-ci.yml

-image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.3.3-golang-1.8-git-2.7-phantomjs-2.1-node-7.1-postgresql-9.6"
+image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.3.3-golang-1.8-git-2.13-phantomjs-2.1-node-7.1-postgresql-9.6"
 .default-cache: &default-cache
   key: "ruby-233-with-yarn"
@@ -522,7 +522,7 @@ karma:
   <<: *dedicated-runner
   <<: *except-docs
   <<: *pull-cache
-  image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.3.3-golang-1.8-git-2.7-chrome-59.0-node-7.1-postgresql-9.6"
+  image: "dev.gitlab.org:5005/gitlab/gitlab-build-images:ruby-2.3.3-golang-1.8-git-2.13-chrome-59.0-node-7.1-postgresql-9.6"
   stage: test
   variables:
     BABEL_ENV: "coverage"

doc/install/installation.md

@@ -80,7 +80,7 @@ Make sure you have the right version of Git installed
     # Install Git
     sudo apt-get install -y git-core
-    # Make sure Git is version 2.8.4 or higher
+    # Make sure Git is version 2.13.0 or higher
     git --version
 Is the system packaged Git too old? Remove it and compile from source.