go back to using git protocol

Author: BRONSOLO

.gitmodules

@@ -1,6 +1,6 @@
 [submodule "submodules/mplexporter"]
 	path = submodules/mplexporter
-	url = git@github.com:mpld3/mplexporter.git
+	url = git://github.com/mpld3/mplexporter.git
 [submodule "submodules/chunked_requests"]
 	path = submodules/chunked_requests
-	url = git@github.com:chriddyp/chunked_requests.git
+	url = git://github.com/chriddyp/chunked_requests.git