fix(react-container-message-composer): Fix failing tests

Author: bzang

__mocks__/sound-mock.js

@@ -0,0 +1,2 @@
+// Return an object to emulate sound modules
+export default {};

jest.config.json

@@ -7,6 +7,7 @@
   "transformIgnorePatterns": ["<rootDir>/node_modules/"],
   "moduleNameMapper": {
     "^.+\\.(css|less)$": "<rootDir>/__mocks__/style-mock.js",
+    "^.+\\.(mp3|wav)$": "<rootDir>/__mocks__/sound-mock.js",
     "^.+\\.(gif|ttf|eot|svg|png|jpg)$": "<rootDir>/__mocks__/file-mock.js",
     "@ciscospark/(.*)": "<rootDir>/packages/node_modules/@ciscospark/$1/src"
   },