Fix root submodules task and for older versions of git

External/Rakefile

@@ -23,7 +23,7 @@ end
 
 task :update_submodules do
   if executable_exists? "git"
-    system %{cd .. && git submodule update --init}
+    system %{cd .. && git submodule init && git submodule update}
   else
     puts "Git not installed"
     rake abort

Rakefile

@@ -102,7 +102,7 @@ end
 
 task :submodules do
     if executable_exists? "git"
-        system %{cd .. && git submodule update --init}
+        system %{git submodule init && git submodule update}
     else
         puts "Git not installed"
         rake abort