Tweak makefile to get GERRIT_BRANCH if defined

The way Jenkins jobs are checked out, the branch is not active, but
it is defined in the GERRIT_BRANCH env var. So if we can find that
defined, then that's the branch that should be built. If not, we can
just build the current branch.

Signed-off-by: Eric Ball <eball@linuxfoundation.org>
Change-Id: I2e149661f7a7f07ba3674cc60be4daaf396b08fe
diff --git a/Makefile b/Makefile
index eed77bc..447e858 100644
--- a/Makefile
+++ b/Makefile
@@ -40,7 +40,14 @@
 SPHINXBUILD  ?= sphinx-build
 SOURCEDIR    ?= .
 BUILDDIR     ?= _build
-BRANCH       ?= $(shell git branch --show-current)
+
+# If running on Jenkins, we need to pick up the GERRIT_BRANCH env var.
+# Otherwise, we can simply use the current branch.
+ifdef GERRIT_BRANCH
+  BRANCH := $(GERRIT_BRANCH)
+else
+  BRANCH := $(shell git branch --show-current)
+endif
 
 # Other repos with documentation to include.
 # edit the `git_refs` file with the commit/tag/branch that you want to use
diff --git a/VERSION b/VERSION
index 0e83a9a..a1a4224 100644
--- a/VERSION
+++ b/VERSION
@@ -1 +1 @@
-2.13.2
+2.13.3