Bug 1530372 - Part 5: Add 'nursery-bigints' to fuzz-flags.txt. r=gkw

Differential Revision: https://phabricator.services.mozilla.com/D58520

--HG--
extra : moz-landing-system : lando

js/src/shell/fuzz-flags.txt

@@ -48,6 +48,8 @@
 --no-native-regexp
 --nursery-strings=off
 --nursery-strings=on
+--nursery-bigints=off
+--nursery-bigints=on
 --parser-deferred-alloc
 --spectre-mitigations=off
 --spectre-mitigations=on