MNT: Silence some pandas warnings

Pandas 0.21 started warning about getting the behavior we exactly
expect, so filter out those warnings.

siphon/simplewebservice/wyoming.py

@@ -4,13 +4,16 @@
 """Read upper air data from the Wyoming archives."""
 
 from io import StringIO
+import warnings
 
 from bs4 import BeautifulSoup
 import numpy as np
 import pandas as pd
 from .._tools import get_wind_components
 from ..http_util import HTTPEndPoint
 
+warnings.filterwarnings('ignore', 'Pandas doesn\'t allow columns to be created', UserWarning)
+
 
 class WyomingUpperAir(HTTPEndPoint):
     """Download and parse data from the University of Wyoming's upper air archive."""