Marke SingletonByRef functions scope

Platform dependencies aren't supported according to the dub
documentation, that states: "this setting does not support platform
suffixes".

dub test with dub 1.34.0 produces a warning:

"dependencies-linux: Key is not a valid member of this section.
Did you mean: dependencies"

Then the build fails because it cannot find modules defined in the
dependency.

dub.json

@@ -13,10 +13,7 @@
 		"tanya:meta": "*",
 		"tanya:os": "*",
 		"tanya:middle": "*",
-		"tanya:test": "*"
-	},
-
-	"dependencies-linux": {
+		"tanya:test": "*",
 		"mir-linux-kernel": "~>1.0.0"
 	},
 

source/tanya/algorithm/iteration.d

@@ -109,7 +109,7 @@ private struct SingletonByRef(E)
         this.element = &element;
     }
 
-    @property ref inout(E) front() inout return
+    @property ref inout(E) front() inout return scope
     in
     {
         assert(!empty);
@@ -148,7 +148,7 @@ private struct SingletonByRef(E)
         return typeof(this)(*this.element);
     }
 
-    ref inout(E) opIndex(size_t i) inout return
+    ref inout(E) opIndex(size_t i) inout return scope
     in
     {
         assert(!empty);