fix: add missing prng option

PR-URL: #12566
Reviewed-by: Athan Reines <kgryte@gmail.com>

Author: Planeshifter

lib/node_modules/@stdlib/random/streams/randn/docs/types/index.d.ts

@@ -58,6 +58,11 @@ interface Options {
 	*/
 	name?: 'improved-ziggurat' | 'box-muller';
 
+	/**
+	* Pseudorandom number generator which generates uniformly distributed pseudorandom numbers.
+	*/
+	prng?: random.PRNG;
+
 	/**
 	* Pseudorandom number generator seed.
 	*/