deps: Upgrade watcher

With a recent Dart SDK from Flutter main, this is required in
order for build_runner to work.  Otherwise it gives an error
like (reformatted):

    Failed to build build_runner:build_runner:
    ../../.pub-cache/hosted/pub.dev/watcher-1.0.2/lib/src/constructable_file_system_event.dart:7:57:
      Error: The class 'FileSystemEvent' can't be extended, implemented,
      or mixed in outside of its library because it's a sealed class.
    abstract class _ConstructableFileSystemEvent implements FileSystemEvent {

Author: gnprice

pubspec.lock

@@ -929,10 +929,10 @@ packages:
     dependency: transitive
     description:
       name: watcher
-      sha256: "6a7f46926b01ce81bfc339da6a7f20afbe7733eff9846f6d6a5466aa4c6667c0"
+      sha256: "3d2ad6751b3c16cf07c7fca317a1413b3f26530319181b37e3b9039b84fc01d8"
       url: "https://pub.dev"
     source: hosted
-    version: "1.0.2"
+    version: "1.1.0"
   web_socket_channel:
     dependency: transitive
     description: