python 3 compatibility: import guard around ConfigParser

In python3 `ConfigParser` has become `configparser`. Added
an import guard that aliases it back to the old name.

contrib/inventory/digital_ocean.py

@@ -138,9 +138,13 @@ import sys
 import re
 import argparse
 from time import time
-import ConfigParser
 import ast
 
+try:
+    import ConfigParser
+except ImportError:
+    import configparser as ConfigParser
+
 try:
     import json
 except ImportError: