Fix Flow (1/2)

Define missing "before" function so that it does not cause flow
to fail.

Author: grabbou

local-cli/__tests__/fs-mock-test.js

@@ -17,6 +17,7 @@
 
 declare var jest: any;
 declare var describe: any;
+declare var expect: any;
 declare var it: any;
 
 jest.mock('fs');