Build: update miniupnp submodule

f21df05 was never supposed to be merged into the master branch.
fluffypony merged #3670 before #3668 was rebased and resolved.

Note: the cherry-picked commit hashes are now invalid because #3670
was merged before #3668 was rebased with the updated repo location.

.gitmodules

@@ -4,5 +4,5 @@
 	branch = monero
 [submodule "external/miniupnp"]
 	path = external/miniupnp
-	url = https://github.com/anonimal/miniupnp
+	url = https://github.com/monero-project/miniupnp
 	branch = monero