docs: fix return value

Signed-off-by: Athan <[email protected]>

Author: kgryte

lib/node_modules/@stdlib/blas/ext/last-index-of/README.md

@@ -168,7 +168,7 @@ var out = lastIndexOf.assign( x, 2.0, y );
 // returns <ndarray>
 
 var idx = out.get();
-// returns -1
+// returns 3
 
 var bool = ( out === y );
 // returns true