docs: fix building

Author: sgratzl

docs/source/conf.py

@@ -58,7 +58,7 @@
 
 # General information about the project.
 project = "upsetjs_jupyter_widget"
-copyright = "2020, Samuel Gratzl"
+copyright = "2021, Samuel Gratzl"
 author = "Samuel Gratzl"
 
 # The version info for the project you're documenting, acts as replacement for
@@ -218,7 +218,7 @@ def setup(app):
     def add_scripts(app):
         for fname in ["helper.js", "embed-bundle.js"]:
             if not os.path.exists(os.path.join(source, "_static", fname)):
-                app.warn("missing javascript file: %s" % fname)
+                print("missing javascript file: %s" % fname)
             app.add_js_file(fname)
 
     app.connect("builder-inited", add_scripts)