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/lint/lint-assertions.py

@@ -12,7 +12,7 @@ import subprocess
 
 def git_grep(params: [], error_msg: ""):
     try:
-        output = subprocess.check_output(["git", "grep", *params], universal_newlines=True, encoding="utf8")
+        output = subprocess.check_output(["git", "grep", *params], text=True, encoding="utf8")
         print(error_msg)
         print(output)
         return 1