Make _.at support shortcut fusion in a chain sequence when operating on an array and selecting a single index. [closes #1636]

lodash.js

@@ -13893,6 +13893,13 @@
       };
     });
 
+    LazyWrapper.prototype.at = rest(function(paths) {
+      paths = baseFlatten(paths);
+      return (paths.length == 1 && isIndex(paths[0]))
+        ? this.slice(paths[0], paths[0] + 1)
+        : new LazyWrapper(this);
+    });
+
     LazyWrapper.prototype.compact = function() {
       return this.filter(identity);
     };