fix typo: "javscript"

tornado/escape.py

@@ -82,7 +82,7 @@ def json_encode(value):
     # JSON permits but does not require forward slashes to be escaped.
     # This is useful when json data is emitted in a <script> tag
     # in HTML, as it prevents </script> tags from prematurely terminating
-    # the javscript.  Some json libraries do this escaping by default,
+    # the javascript.  Some json libraries do this escaping by default,
     # although python's standard library does not, so we do it here.
     # http://stackoverflow.com/questions/1580647/json-why-are-forward-slashes-escaped
     return json.dumps(value).replace("</", "<\\/")