Update http links to https

Change-Id: Ie2de4c427f234495c77b57ea0ce31cf41fa46ff1
GitHub-Last-Rev: e2d1d79ba359738ce6725a4627de674f9d5eb850
GitHub-Pull-Request: golang/gddo#568
Reviewed-on: https://go-review.googlesource.com/126575
Reviewed-by: Tuo Shan <shantuo@google.com>
diff --git a/README.markdown b/README.markdown
index 7fadcb2..f1b019a 100644
--- a/README.markdown
+++ b/README.markdown
@@ -1,6 +1,6 @@
-This project is the source for http://godoc.org/
+This project is the source for https://godoc.org/
 
-[![GoDoc](https://godoc.org/github.com/golang/gddo?status.svg)](http://godoc.org/github.com/golang/gddo)
+[![GoDoc](https://godoc.org/github.com/golang/gddo?status.svg)](https://godoc.org/github.com/golang/gddo)
 [![Build
 Status](https://travis-ci.org/golang/gddo.svg?branch=master)](https://travis-ci.org/golang/gddo)