Assert text files are in utf8 (#350)

Read and write text files with utf8 encoding.

Signed-off-by: Bobby Noelte <b0661n0e17e@gmail.com>

scripts/generate_openapi_md.py

@@ -286,7 +286,7 @@ def main():
         openapi_md = generate_openapi_md()
         if args.output_file:
             # Write to file
-            with open(args.output_file, "w") as f:
+            with open(args.output_file, "w", encoding="utf8") as f:
                 f.write(openapi_md)
         else:
             # Write to std output