Update domain.py

Correct empty lines in imports

sympde/topology/domain.py

@@ -12,13 +12,13 @@
 
 from sympy import Integer
 from sympy.core.singleton import Singleton
-from sympde.old_sympy_utilities import is_sequence, with_metaclass
 from sympy.core import Basic, symbols
 from sympy.core.containers import Tuple
 from sympy.tensor import IndexedBase, Indexed
 from sympy.core import Add, Mul, Pow
 from sympy.core.expr import AtomicExpr
 
+from sympde.old_sympy_utilities import is_sequence, with_metaclass
 from sympde.core.basic import CalculusFunction
 from .basic import BasicDomain, InteriorDomain, Boundary, Union, Connectivity
 from .basic import Interval, Interface, CornerBoundary, CornerInterface