update the if condition to check successful login

due to i18n, the text "Sign Out" might not appear in the returned html. 

The <i>a<i> tag for logging out:
```
<a href="https://accounts.wsj.com/logout?target=">登出</a>
```

recipes/wsj.recipe

@@ -148,7 +148,7 @@ class WSJ(BasicNewsRecipe):
             self.log('Performing login callback...')
             res = br.submit()
             self.wsj_itp_page = raw = res.read()
-            if b'>Sign Out<' not in raw:
+            if b'logout' not in raw:
                 raise ValueError(
                     'Failed to login (callback URL failed), check username and password')
             return br