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/rpc_users.py

@@ -53,13 +53,13 @@ class HTTPBasicsTest(BitcoinTestFramework):
 
         # Generate RPCAUTH with specified password
         self.rt2password = "8/F3uMDw4KSEbw96U3CA1C4X05dkHDN2BPFjTgZW4KI="
-        p = subprocess.Popen([sys.executable, gen_rpcauth, 'rt2', self.rt2password], stdout=subprocess.PIPE, universal_newlines=True)
+        p = subprocess.Popen([sys.executable, gen_rpcauth, 'rt2', self.rt2password], stdout=subprocess.PIPE, text=True)
         lines = p.stdout.read().splitlines()
         rpcauth2 = lines[1]
 
         # Generate RPCAUTH without specifying password
         self.user = ''.join(SystemRandom().choice(string.ascii_letters + string.digits) for _ in range(10))
-        p = subprocess.Popen([sys.executable, gen_rpcauth, self.user], stdout=subprocess.PIPE, universal_newlines=True)
+        p = subprocess.Popen([sys.executable, gen_rpcauth, self.user], stdout=subprocess.PIPE, text=True)
         lines = p.stdout.read().splitlines()
         rpcauth3 = lines[1]
         self.password = lines[3]