Strip trailing whitespaces @ EOL when dumping FST

It's a workaround for PyCQA/redbaron#190

migrate.py

@@ -235,6 +235,11 @@ def write_text_into_file(path, text):
         return f.write(text)
 
 
+def write_fst_into_file(path, fst):
+    """Dump fst into the given file path."""
+    write_text_into_file(path, fst.dumps().rstrip())
+
+
 @contextlib.contextmanager
 def working_directory(target_dir):
     """Temporary change dir to the target and change back on exit."""
@@ -788,13 +793,13 @@ def fst_rewrite_session(src_path, dst_path):
 
     yield mod_fst
 
-    new_mod_src_text = mod_fst.dumps()
+    new_mod_src_text = mod_fst.dumps().rstrip()
 
     if src_path == dst_path and mod_src_text == new_mod_src_text:
         return
 
     logger.info('Rewriting plugin references in %s', dst_path)
-    write_text_into_file(dst_path, new_mod_src_text)
+    write_fst_into_file(dst_path, mod_fst)
 
 
 def read_module_txt_n_fst(path):