Fix YAML dumping style for consistency in output files.

The default_flow_style=None will let it
use a single line for things like [1.3, 4.0, 4.45].
Which should look more like we expected.

It's a bit clunky that we have to read the yaml, modify the dicts, and dump the yaml, but this should
make the changes less obnoxious.

Author: rwest

rmgpy/rmg/main.py

@@ -1263,10 +1263,10 @@ def execute(self, initialize=True, **kwargs):
                     annotated_content['species'] = content['species']
 
                     with open(chem_yaml_path, 'w') as output_f:
-                        yaml.dump(content, output_f, sort_keys=False)
+                        yaml.dump(content, output_f, sort_keys=False, default_flow_style=None)
 
                     with open(annotated_yaml_path, 'w') as output_f:
-                        yaml.dump(annotated_content, output_f, sort_keys=False)
+                        yaml.dump(annotated_content, output_f, sort_keys=False, default_flow_style=None)
 
             else:  # gas phase only
                 self.generate_cantera_files(os.path.join(self.output_directory, "chemkin", "chem.inp"))