doc: fix links in YAML metadata of assert.md

PR-URL: #18670
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

doc/api/assert.md

@@ -113,7 +113,9 @@ changes:
     description: Enumerable symbol properties are now compared.
   - version: v9.0.0
     pr-url: https://github.com/nodejs/node/pull/15036
-    description: NaN is now compared using the [SameValueZero][] comparison.
+    description: NaN is now compared using the
+                 [SameValueZero](https://tc39.github.io/ecma262/#sec-samevaluezero)
+                 comparison.
   - version: v8.5.0
     pr-url: https://github.com/nodejs/node/pull/15001
     description: Error names and messages are now properly compared
@@ -461,7 +463,9 @@ changes:
     description: -0 and +0 are not considered equal anymore.
   - version: v9.0.0
     pr-url: https://github.com/nodejs/node/pull/15036
-    description: NaN is now compared using the [SameValueZero][] comparison.
+    description: NaN is now compared using the
+                 [SameValueZero](https://tc39.github.io/ecma262/#sec-samevaluezero)
+                 comparison.
   - version: v9.0.0
     pr-url: https://github.com/nodejs/node/pull/15001
     description: Error names and messages are now properly compared