Ensure flutter format and fix offending files (#80)

The current Travis script will only print offending files, but won’t fail the build. Added `--set-exit-if-changed` to fix that.

Also, simplified the call from using `grep` and `xargs` to simple `flutter format .`, which recurses directories.

Lastly, fixed offending files that needed `dartfmt`. (But not in the directories that aren’t covered by `travis_script.sh`.

place_tracker/lib/place_map.dart

@@ -224,7 +224,6 @@ class PlaceMapState extends State<PlaceMap> {
 
   void _confirmAddPlace(BuildContext context) async {
     if (_pendingMarker != null) {
-
       // Create a new Place and map it to the marker we just added.
       final Place newPlace = Place(
         id: Uuid().v1(),