googletest.cmd: cd back to original dir when done

Change back to the original directory when done. All the other ext/*.cmd
files do this.
diff --git a/ext/googletest.cmd b/ext/googletest.cmd
index f080a0f..ebdc3a7 100755
--- a/ext/googletest.cmd
+++ b/ext/googletest.cmd
@@ -13,3 +13,4 @@
 cd build
 cmake -G Ninja -DCMAKE_BUILD_TYPE=Release -DBUILD_GMOCK=OFF ..
 cmake --build .
+cd ../..