It seems googletest must be a subdirectory, so move it to tests.

Former-commit-id: 1b2739393299e812480a9128248591b830775788

.gitmodules

@@ -9,6 +9,8 @@ url=https://github.com/libigl/nanogui.git
 	url = https://github.com/embree/embree.git
 
 [submodule "external/googletest"]
-    pqth = external/googletest
 	url = https://github.com/google/googletest.git
 	path = external/googletest
+[submodule "tests/googletest"]
+	path = tests/googletest
+	url = https://github.com/google/googletest.git

tests/googletest

@@ -0,0 +1 @@
+Subproject commit de411c3e80120f8dcc2a3f4f62f3ca692c0431d7