updating test for a css feature that still requires vendor prefix

Author: weaverryan

fixtures/css/autoprefixer_test.css

@@ -1,3 +1,3 @@
-:fullscreen a {
-    display: flex
+.example {
+  backdrop-filter: blur(10px);
 }

test/functional.js

@@ -1037,15 +1037,15 @@ module.exports = {
                 // check that the autoprefixer did its work!
                 webpackAssert.assertOutputFileContains(
                     'styles.css',
-                    '-webkit-full-screen'
+                    '-webkit-backdrop-filter'
                 );
 
                 // check that the .postcss file was also processed
                 // correctly (it also @import the autoprefixer_test.css
                 // file)
                 webpackAssert.assertOutputFileContains(
                     'postcss.css',
-                    '-webkit-full-screen'
+                    '-webkit-backdrop-filter'
                 );
 
                 done();