Compatibility for upstream xtensor change

The upstream change broke the build: xtensor-stack/xtensor@da7de15

Add pycontainer::is_contiguous to make xtensor happy.

Author: yungyuc

include/xtensor-python/pycontainer.hpp

@@ -93,6 +93,7 @@ namespace xt
         void reshape(S&& shape, layout_type layout = base_type::static_layout);
 
         layout_type layout() const;
+        bool is_contiguous() const noexcept;
 
         using base_type::operator();
         using base_type::operator[];
@@ -442,6 +443,16 @@ namespace xt
         }
     }
 
+    /**
+     * Return whether or not the container uses contiguous buffer
+     * @return Boolean for contiguous buffer
+     */
+    template <class D>
+    inline bool pycontainer<D>::is_contiguous() const noexcept
+    {
+        return layout_type::dynamic != layout();
+    }
+
     /**
      * Import the numpy Python module.
      */