Fix formatting.

pennylane_lightning/core/_serialize.py

@@ -255,7 +255,7 @@ def map_wire(wire: int):
 
     def _pauli_sentence(self, observable, wires_map: dict = None):
         """Serialize a :class:`pennylane.pauli.PauliSentence` into a Hamiltonian."""
-        # Trivial Pauli sentences' items is empty, cannot unpack 
+        # Trivial Pauli sentences' items is empty, cannot unpack
         if not observable:
             return self.hamiltonian_obs(np.array([0.0]).astype(self.rtype), [self._ob(Identity(0))])
         pwords, coeffs = zip(*observable.items())