Typos in some city names

In the [Constants.java](https://github.com/IBM/sample-app-mod/blob/main/src/main/java/com/acme/modres/Constants.java) file, there are some cities with typos, like: 

```
  public final static String BACELONA_WEATHER_FILE = "barcelona.json";
  public final static String SAN_FRANCESCO_WEATHER_FILE = "sanfran.json";
```

It should be BARCELONA and SAN_FRANCISCO.