Make InfiniteIterable strong mode compliant

.analysis_options

@@ -0,0 +1,7 @@
+# This file allows you to configure the Dart analyzer.
+#
+# The commented part below is just for inspiration. Read the guide here:
+#   https://www.dartlang.org/guides/language/analysis-options
+
+ analyzer:
+   strong-mode: true

lib/src/infinite_iterable.dart

@@ -29,7 +29,8 @@ abstract class InfiniteIterable<T> extends IterableBase<T> {
 
   bool every(bool f(T element)) => throw new UnsupportedError('every');
 
-  bool fold(initialValue, combine(previousValue, T element)) =>
+  @override
+  V fold<V>(V initialValue, combine(V previousValue, T element)) =>
       throw new UnsupportedError('fold');
 
   void forEach(void f(T element)) => throw new UnsupportedError('forEach');

pubspec.yaml

@@ -1,5 +1,5 @@
 name: quiver_iterables
-version: 1.0.0
+version: 1.0.0+1
 authors:
 - Justin Fagnani <justinfagnani@google.com>
 - Yegor Jbanov <yjbanov@google.com>