Use HTTPS Git access for IKVM sub-module to please Travis.

.gitmodules

@@ -1,6 +1,6 @@
 [submodule "ikvm"]
 	path = ikvm
-	url = git@github.com:mono/ikvm-fork.git
+	url = https://github.com/mono/ikvm-fork.git
 [submodule "catch"]
 	path = catch
 	url = https://github.com/philsquared/Catch.git