Fix readerfooter_spec (#3326)

My bad, leftover from #3323 but not caught due to some Travis → CircleCI migration birth pains.

spec/unit/readerfooter_spec.lua

@@ -577,7 +577,7 @@ describe("Readerfooter module", function()
 
         assert.falsy(footer.has_no_mode)
         assert.truthy(readerui.view.footer_visible)
-        assert.is.same(21, footer:getHeight())
+        assert.is.same(24, footer:getHeight())
     end)
 
     it("should return correct footer height when all modes are disabled", function()
@@ -595,7 +595,7 @@ describe("Readerfooter module", function()
 
         assert.truthy(footer.has_no_mode)
         assert.falsy(readerui.view.footer_visible)
-        assert.is.same(21, footer:getHeight())
+        assert.is.same(24, footer:getHeight())
     end)
 
     it("should disable footer if settings.disabled is true", function()