Flutter_map: stable channel compatibility

[johnpryan]

Fix compatibility issues with beta channel

[DavidKuennen]

It's the stable channel by now, so the name doesn't match anymore. ;-)

[johnpryan]

merging with https://github.com/johnpryan/flutter_map/issues/353

[MichalMisiaszek]

Any ETA on new version ? Unfortunately flutter_image on which map and plugin depends are failing too.
```file:///Users/michal/Development/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_image-1.0.0/lib/network.dart:75:31: Error: The argument type 'Null Function(StringBuffer)' can't be assigned to the parameter type 'Iterable Function()'.

• 'StringBuffer' is from 'dart:core'.
• 'Iterable' is from 'dart:core'.
• 'DiagnosticsNode' is from 'package:flutter/src/foundation/diagnostics.dart' ('file:///Users/michal/Development/flutter/packages/flutter/lib/src/foundation/diagnostics.dart').
  Try changing the type of the parameter, or casting the argument to 'Iterable Function()'.
  informationCollector: (StringBuffer information) {
  ^
  file:///Users/michal/Development/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_image-1.0.0/lib/network.dart:168:65: Error: The argument type 'String' can't be assigned to the parameter type 'DiagnosticsNode'.
• 'DiagnosticsNode' is from 'package:flutter/src/foundation/diagnostics.dart' ('file:///Users/michal/Development/flutter/packages/flutter/lib/src/foundation/diagnostics.dart').
  Try changing the type of the parameter, or casting the argument to 'DiagnosticsNode'.
  context: '$runtimeType failed to load ${instructions.uri}',

[MichalMisiaszek]

Perfect ! Thanks John, this is really great plugin.

[johnpryan]

😎 thanks for your patience, everyone

[johnpryan]

Released in version 0.5.6

[MichalMisiaszek]

Works ! :)