scripted-diff: Use new python 3.7 keywords

-BEGIN VERIFY SCRIPT-
 sed -i 's/universal_newlines/text/g' $(git grep -l universal_newlines)
-END VERIFY SCRIPT-

test/functional/tool_wallet.py

@@ -37,7 +37,7 @@ class ToolWalletTest(BitcoinTestFramework):
         if not self.options.descriptors and 'create' in args:
             default_args.append('-legacy')
 
-        return subprocess.Popen([binary] + default_args + list(args), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, universal_newlines=True)
+        return subprocess.Popen([binary] + default_args + list(args), stdin=subprocess.PIPE, stdout=subprocess.PIPE, stderr=subprocess.PIPE, text=True)
 
     def assert_raises_tool_error(self, error, *args):
         p = self.bitcoin_wallet_process(*args)