Address Pylint new unspecified-encoding warning

A new warning appeared from pylint when calling "tox -e lint" on the
"develop" branch with id "unspecified-encoding",
I read about the warning and it make sense.

Read more about the warning here:
pylint-dev/pylint#3826

Signed-off-by: Martin Vrachev <[email protected]>

Author: MVrachev

tuf/developer_tool.py

@@ -749,7 +749,7 @@ def _save_project_configuration(metadata_directory, targets_directory,
     project_config['public_keys'][key] = key_metadata
 
   # Save the actual file.
-  with open(project_filename, 'wt') as fp:
+  with open(project_filename, 'wt', encoding='utf8') as fp:
     json.dump(project_config, fp)
 
 

tuf/unittest_toolbox.py

@@ -116,7 +116,7 @@ def _destroy_temp_file():
   def make_temp_data_file(self, suffix='', directory=None, data = 'junk data'):
     """Returns an absolute path of a temp file containing data."""
     temp_file_path = self.make_temp_file(suffix=suffix, directory=directory)
-    temp_file = open(temp_file_path, 'wt')
+    temp_file = open(temp_file_path, 'wt', encoding='utf8')
     temp_file.write(data)
     temp_file.close()
     return temp_file_path