Fixed clientside emoji tests leaving behind a temporary file (#3691)

webapp/.eslintrc.json

@@ -24,7 +24,8 @@
         "describe": true,
         "it": true,
         "expect": true,
-        "before": true
+        "before": true,
+        "after": true
     },
     "rules": {
         "array-bracket-spacing": [2, "never"],

webapp/tests/client_emoji.test.jsx

@@ -17,6 +17,10 @@ describe('Client.Emoji', function() {
         fs.writeFileSync(testGif, buffer);
     });
 
+    after(function() {
+        fs.unlinkSync('test.gif');
+    });
+
     it('addEmoji', function(done) {
         TestHelper.initBasic(() => {
             const name = TestHelper.generateId();