Upgrade to avoid build errors/warnings

[ghost]

Got this error when trying to build flutter application with dependency on this plugin.

WARNING: API 'variant.getMergeAssets()' is obsolete and has been replaced with 'variant.getMergeAssetsProvider()'.
It will be removed at the end of 2019.
For more information, see https://d.android.com/r/tools/task-configuration-avoidance.
REASON: Called from: /home/kvester/opt/flutter/packages/flutter_tools/gradle/flutter.gradle:605
WARNING: Debugging obsolete API calls can take time during configuration. It's recommended to not keep it on at all times.
WARNING: API 'variantOutput.getProcessResources()' is obsolete and has been replaced with 'variantOutput.getProcessResourcesProvider()'.
It will be removed at the end of 2019.
For more information, see https://d.android.com/r/tools/task-configuration-avoidance.
REASON: Called from: /home/kvester/opt/flutter/packages/flutter_tools/gradle/flutter.gradle:614
WARNING: Debugging obsolete API calls can take time during configuration. It's recommended to not keep it on at all times.

Updating the dependencies seems to have fixed it.

[ghost]

I also fixed it so that the channel is called from the UIThread

[KarimAbdo]

Could you resolve the conflict to merge this ?