Bug 1333591 - Add foundational to the en-US dictionary. r=ehsan

extensions/spellcheck/locales/en-US/hunspell/en-US.dic

@@ -1,4 +1,4 @@
-52348
+52349
 0/nm
 0th/pt
 1/n1
@@ -26862,6 +26862,7 @@ foulmouthed
 foulness/M
 found/FSDG
 foundation/SM
+foundational
 founded/U
 founder/GMDS
 foundling/SM