Update _dataframe_client.py (influxdata#593)

dragoshenron · xginn8 · commit 472de65b99bb · 2018-06-10T22:13:22.000-04:00
Permanent error "NameError: name 'to_datetime' is not defined". Reason: to_datetime is a function defined in pandas not a method on a DataFrame. (see: https://stackoverflow.com/questions/48387878/attributeerror-dataframe-object-has-no-attribute-to-datetime) Tested with Python 3.5.3 and Pandas 0.23.0
diff --git a/influxdb/_dataframe_client.py b/influxdb/_dataframe_client.py
@@ -236,7 +236,7 @@ def _convert_dataframe_to_json(dataframe,
             field_columns = list(
                 set(dataframe.columns).difference(set(tag_columns)))
 
-        dataframe.index = dataframe.index.to_datetime()
+        dataframe.index = pd.to_datetime(dataframe.index)
         if dataframe.index.tzinfo is None:
             dataframe.index = dataframe.index.tz_localize('UTC')
 
