Fix QueuePool size timeout error.

config.py

@@ -31,6 +31,8 @@ class DevelopmentConfig(Config):
     DEBUG = True
 
     ''' ### Flask-SQLAlchemy ### '''
+    SQLALCHEMY_ENGINE_OPTIONS = {'pool_size': 30,
+                                 'pool_timeout': 30}
     SQLALCHEMY_DATABASE_URI = 'postgresql://{}:{}@db/{}'.format(
         os.environ.get('POSTGRES_USER'),
         os.environ.get('POSTGRES_PASSWORD'),