content/go1.15-proposals.article: revert "use relative links for other blog articles"

This reverts CL 216626 (commit 8bf1296992b6579acabcba62cc6cd0efe039c38a).

We cannot rely on relative links in blog posts to stay relative to
blog.golang.org, because blog posts are also embedded on golang.org.
This change caused those links to point to
https://golang.org/go2-here-we-come, which is 404.

Fixes golang/go#36930
Updates golang/go#36944

Change-Id: Ie5ca8f112ff6465328d258b283d540c07e909a54
Reviewed-on: https://go-review.googlesource.com/c/blog/+/217239
Reviewed-by: Robert Griesemer <gri@golang.org>
diff --git a/content/go1.15-proposals.article b/content/go1.15-proposals.article
index 62a3034..01bfe48 100644
--- a/content/go1.15-proposals.article
+++ b/content/go1.15-proposals.article
@@ -9,7 +9,7 @@
 
 We are close to the Go 1.14 release, planned for February assuming all goes
 well, with an RC1 candidate almost ready. Per the process outlined in the
-[[/go2-here-we-come][Go 2, here we come!]] blog post,
+[[https://blog.golang.org/go2-here-we-come][Go 2, here we come!]] blog post,
 it is again the time in our development and release cycle to consider if and
 what language or library changes we might want to include for our next release,
 Go 1.15, scheduled for August of this year.
@@ -81,7 +81,7 @@
 to have the proposals implemented at the beginning of the Go 1.15 release cycle
 (at or shortly after the Go 1.14 release) so that there is plenty of time to
 gather experience and provide feedback. Per the
-[[/go2-here-we-come][proposal evaluation process]],
+[[https://blog.golang.org/go2-here-we-come][proposal evaluation process]],
 the final decision will be made at the end of the development cycle, at the
 beginning of May, 2020.