Rename file instead of re-writing

Author: keelerm84

ldclient/testing/test_file_data_source.py

@@ -117,8 +117,8 @@ def make_temp_file(content):
     return path
 
 def replace_file(path, content):
-    with open(path, 'w') as f:
-        f.write(content)
+    temp_path = make_temp_file(content)
+    os.rename(temp_path, path)
 
 def test_does_not_load_data_prior_to_start():
     path = make_temp_file('{"flagValues":{"key":"value"}}')