Corrected method name

The previous commit used generate_resonance_isomers.
The current name is generate_resonance_structures, which
this commit changes it to.

thermo_val/model.py

@@ -25,7 +25,7 @@ def predict_thermo(self, smiles):
 
         if self.kernel_type == 'GA':
             spec = Species().fromSMILES(smiles)
-            spec.generate_resonance_isomers()
+            spec.generate_resonance_structures()
 
             thermo = self.kernel.getThermoDataFromGroups(spec)