Encode parameter yaml as utf-8 to fix error when running on windows (#333)

Simple Windows compatibility fix - adds UTF-8 encoding when loading YAML parameter files.

Fixes #330

Author: noman404

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    fixed:
+    - Issue of running on windows because of not having UTF-8 encoding.

policyengine_core/parameters/helpers.py

@@ -41,7 +41,7 @@ def _compose_name(path, child_name=None, item_name=None):
 
 
 def _load_yaml_file(file_path):
-    with open(file_path, "r") as f:
+    with open(file_path, "r", encoding="utf-8") as f:
         try:
             return config.yaml.load(f, Loader=config.Loader)
         except (