Common. Improve column selection (removes warning)

cfatools/logreader/common.py

@@ -85,7 +85,7 @@ class Reader:
 
         """
         if variable in df.columns:
-            df = df[[variable]]
+            df = df.loc[:, [variable]]
             df.rename(columns={variable: 'value'}, inplace=True)
         else:
             raise ValueError("There is no [" + variable + "] column in this dataframe."