Add explicit type to for-in loop (#16)

Workaround for dart-lang/sdk#31884 in the
dev.17.0 version of the SDK.

Author: natebosch

lib/src/strongly_connected_components.dart

@@ -40,7 +40,7 @@ List<List<V>> stronglyConnectedComponents<K, V>(
     index++;
     lastVisited.addLast(node);
     onStack.add(nodeKey);
-    for (final next in children(node) ?? const []) {
+    for (final V next in children(node) ?? const []) {
       var nextKey = key(next);
       if (!indexes.containsKey(nextKey)) {
         strongConnect(next);

pubspec.yaml

@@ -1,5 +1,5 @@
 name: graphs
-version: 0.1.0
+version: 0.1.1-dev
 description: Graph algorithms operation an graphs in any representation.
 author: Dart Team <[email protected]>
 homepage: https://github.com/dart-lang/graphs