Fix quoting in docstring.

accountant/models/scheduled_operations.py

@@ -26,7 +26,7 @@ from .operations import Operation
 
 
 class ScheduledOperation(db.Model):
-    "Class used to handle scheduled operations."
+    """Class used to handle scheduled operations."""
     # pylint: disable=invalid-name
     id = db.Column(db.Integer, primary_key=True)
 
@@ -65,7 +65,7 @@ class ScheduledOperation(db.Model):
 
     @classmethod
     def query(cls):
-        "Return base query for this class."
+        """Return base query for this class."""
         return db.session.query(
             cls
         ).order_by(
@@ -75,7 +75,7 @@ class ScheduledOperation(db.Model):
         )
 
     def reschedule(self):
-        "Reschedule a scheduled operation."
+        """Reschedule a scheduled operation."""
         # 1) delete unconfirmed operations for this account.
         db.session.query(
             Operation