fix path to gbench

.gitmodules

@@ -6,4 +6,4 @@
 	url = https://github.com/google/googletest.git
 [submodule "3rd/gbench"]
 	path = 3rd/gbench
-	url = git@github.com:henrydcase/benchmark.git
+	url = https://github.com/henrydcase/benchmark.git