Bug 1558660 - Adjust fuzz for bugs/391994-1.html on geckoview. r=gbrown

Differential Revision: https://phabricator.services.mozilla.com/D34724

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

layout/reftests/bugs/reftest.list

@@ -800,7 +800,7 @@ skip-if(!winWidget) == 391045.html 391045-ref.html # windows-specific Uniscribe
 == 391412-1b.html 391412-1-ref.html
 == 391909-1.html 391909-1-ref.html
 skip-if(Android) == 391979.html 391979-ref.html
-== 391994-1.html 391994-1-ref.html
+fuzzy-if(geckoview,0-4,0-1) == 391994-1.html 391994-1-ref.html
 == 392047.html 392047-ref.html
 == 392435-1.html 392435-1-ref.html
 == 393330-1.html 393330-1-ref.html