docs: fix typo in thread safety example code (#1100)


diff --git a/docs/thread_safety.md b/docs/thread_safety.md
index 69f369e..d29ba71 100644
--- a/docs/thread_safety.md
+++ b/docs/thread_safety.md
@@ -17,7 +17,7 @@
 
 # Create a new Http() object for every request
 def build_request(http, *args, **kwargs):
-  new_htpp = google_auth_httplib2.AuthorizedHttp(credentials, http=httplib2.Http())
+  new_http = google_auth_httplib2.AuthorizedHttp(credentials, http=httplib2.Http())
   return googleapiclient.http.HttpRequest(new_http, *args, **kwargs)
 service = discovery.build('api_name', 'api_version', requestBuilder=build_request)