Fix yaml env loading

boop.py

@@ -24,7 +24,7 @@ OUTPUT_DIR_NAME = "output"
 # Configure YAML to accept environment variables in metadata files
 # Based on https://stackoverflow.com/a/27232341 solution
 pattern = re.compile(r"^ENV\[\'(.*)\'\]$")
-yaml.add_implicit_resolver("!pathex", pattern)
+yaml.add_implicit_resolver("!pathex", pattern, Loader=yaml.SafeLoader)
 
 
 def pathex_constructor(loader, node):
@@ -33,7 +33,7 @@ def pathex_constructor(loader, node):
     return os.getenv(env_var)
 
 
-yaml.add_constructor("!pathex", pathex_constructor)
+yaml.add_constructor("!pathex", pathex_constructor, yaml.SafeLoader)
 
 
 def list_galleries_in(path):
@@ -43,7 +43,7 @@ def list_galleries_in(path):
         metadata_path = os.path.join(gallery_dir.path, "metadata.yml")
         if os.path.exists(metadata_path):
             with open(metadata_path, "r") as metadata_file:
-                metadata = yaml.load(metadata_file)
+                metadata = yaml.safe_load(metadata_file)
 
         private = False
         url = f"{gallery_dir.name}.html"