runtime: fix typo in debuglog comment

Change-Id: I8a40461b93eab034ed930e0c5e32391f84cdbc5a
Reviewed-on: https://go-review.googlesource.com/c/go/+/170799Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Sebastien Binet <seb.binet@gmail.com>

src/runtime/debuglog.go

@@ -25,7 +25,7 @@ import (
 // heap size.
 const debugLogBytes = 16 << 10
 
-// debugLogStringLimit the the maximum number of bytes in a string.
+// debugLogStringLimit is the maximum number of bytes in a string.
 // Above this, the string will be truncated with "..(n more bytes).."
 const debugLogStringLimit = debugLogBytes / 8