fix(build): fixes broken test.

* Updates flutter to include recent dart changes.

Fixes vanadium/build#81

Change-Id: Id7c42f744bb8bc7dbb317f30bfb48fa63f674575
diff --git a/FLUTTER_VERSION b/FLUTTER_VERSION
index 61c3673..4581483 100644
--- a/FLUTTER_VERSION
+++ b/FLUTTER_VERSION
@@ -1 +1 @@
-199f24ad3ddde9ff6291ec0b6b42972c677fcc7d
+646b5350d1d1c6e39c1c9f1cbb199d958cc6684b
diff --git a/Makefile b/Makefile
index 3dffd14..7129b17 100644
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@
 	@touch $@
 
 .PHONY: clean
-clean:
+clean: depclean
 	@true
 
 .PHONY: depclean
diff --git a/examples/todos/pubspec.lock b/examples/todos/pubspec.lock
index fb60dbd..8f098e5 100644
--- a/examples/todos/pubspec.lock
+++ b/examples/todos/pubspec.lock
@@ -276,7 +276,7 @@
       name: test
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.12.13+1"
+    version: "0.12.13+4"
   typed_data:
     description:
       name: typed_data
@@ -300,7 +300,7 @@
       name: vector_math
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.4.7"
+    version: "2.0.3"
   vm_service_client:
     description:
       name: vm_service_client