Upgrade peewee from 2.10.2 to 3.1.0

Change Database.get_conn() to Database.connection()
ref: <http://docs.peewee-orm.com/en/latest/peewee/changes.html#changes-in-3-0>

zdict/completer.py

@@ -4,7 +4,7 @@
 class DictCompleter:
     def __init__(self):
         self.db = db
-        self.db.get_conn()
+        self.db.connection()
 
     def __del__(self):
         self.db.close()

zdict/dictionary.py

@@ -20,7 +20,7 @@ def __init__(self, args):
         self.db = db
 
         try:
-            self.db.get_conn()
+            self.db.connection()
         except:
             self.db = None
             raise

zdict/tests/test_completer.py

@@ -14,7 +14,7 @@ def test_DictCompleter_db_connect(db):
     '''
     # init
     completer = DictCompleter()
-    assert db.get_conn.called
+    assert db.connection.called
 
     # del
     del completer