content, template: use https instead of protocol-relative URLs

Protocol-relative URLs (//blog.golang.org/...) are redundant, we use
HTTPS everywhere.
Use the https:// scheme instead.

Updates golang/go#17961.

Change-Id: I6be6dd1d85f1093561ce3fa606e1ef37d75a7a60
Reviewed-on: https://go-review.googlesource.com/37883
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/content/constants.article b/content/constants.article
index a001b9a..3a0538f 100644
--- a/content/constants.article
+++ b/content/constants.article
@@ -79,7 +79,7 @@
 
 	"Hello, 世界"
 
-(For much more detail about the representation and interpretation of strings, see [[//blog.golang.org/strings][this blog post]].)
+(For much more detail about the representation and interpretation of strings, see [[https://blog.golang.org/strings][this blog post]].)
 
 What type does this string constant have?
 The obvious answer is `string`, but that is _wrong_.
@@ -180,7 +180,7 @@
 
 .play -edit constants/default3.go /START/,/STOP/
 
-(For more information about how interface values work, see the first sections of [[//blog.golang.org/laws-of-reflection][this blog post]].)
+(For more information about how interface values work, see the first sections of [[https://blog.golang.org/laws-of-reflection][this blog post]].)
 
 In summary, a typed constant obeys all the rules of typed values in Go.
 On the other hand, an untyped constant does not carry a Go type in the same way and can be mixed and matched more freely.
@@ -244,7 +244,7 @@
 prints `10`, as one would expect.
 
 In a related way, floating-point constants may have very high precision, so that arithmetic involving them is more accurate.
-The constants defined in the [[//golang.org/pkg/math][math]] package are given with many more digits than are
+The constants defined in the [[https://golang.org/pkg/math][math]] package are given with many more digits than are
 available in a `float64`. Here is the definition of `math.Pi`:
 
 	Pi	= 3.14159265358979323846264338327950288419716939937510582097494459
diff --git a/template/root.tmpl b/template/root.tmpl
index c77a6d7..17718cc 100644
--- a/template/root.tmpl
+++ b/template/root.tmpl
@@ -10,7 +10,7 @@
 	<title>{{template "title" .}}</title>
 	<link type="text/css" rel="stylesheet" href="/lib/godoc/style.css">
 	<link type="text/css" rel="stylesheet" href="/fonts.css">
-	<link rel="alternate" type="application/atom+xml" title="blog.golang.org - Atom Feed" href="//blog.golang.org/feed.atom" />
+	<link rel="alternate" type="application/atom+xml" title="blog.golang.org - Atom Feed" href="https://blog.golang.org/feed.atom" />
 	<script type="text/javascript">window.initFuncs = [];</script>
 	<style>
 		#sidebar {