Use googletest branch v1.14.x

Change-Id: I09d59a2690bd3c46595f8a4938f520add86e3a63
diff --git a/.gitmodules b/.gitmodules
index 5a4e85a..9b2afbe 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,4 @@
 [submodule "third_party/googletest"]
 	path = third_party/googletest
 	url = https://github.com/google/googletest.git
+	branch = v1.14.x