design/19308-number-literals: fix bad link

Change-Id: I9e453857f3e73fd234c9406a89e0a34d0bb669dc
Reviewed-on: https://go-review.googlesource.com/c/158241
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
diff --git a/design/19308-number-literals.md b/design/19308-number-literals.md
index bb53afd..da877be 100644
--- a/design/19308-number-literals.md
+++ b/design/19308-number-literals.md
@@ -11,7 +11,7 @@
 
    - [golang.org/issue/19308](https://golang.org/issue/19308) (binary integer literals) 
    - [golang.org/issue/12711](https://golang.org/issue/12711) (octal integer literals) 
-   - [golang.org/issue/28493](https://golang.orgissue/28493) (digit separator)
+   - [golang.org/issue/28493](https://golang.org/issue/28493) (digit separator)
    - [golang.org/issue/29008](https://golang.org/issue/29008) (hexadecimal floating point)
 
 ## Abstract