loader: allow YAML templates with .yaml extension

Oficially suggested extension for YAML files is .yaml. Accept it.

Link: https://yaml.org/faq.html
Fixes: #514
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>

src/invoice2data/extract/loader.py

@@ -66,7 +66,7 @@ def read_templates(folder=None):
             with codecs.open(
                 os.path.join(path, name), encoding="utf-8"
             ) as template_file:
-                if name.endswith(".yml"):
+                if name.endswith((".yaml", ".yml")):
                     try:
                         tpl = load(template_file.read(), Loader=SafeLoader)
                     except YAMLError as error: