Update flutter to latest dev channel version (dart-archive#505)

Author: domesticmouse

Dockerfile

@@ -6,7 +6,7 @@ FROM google/dart:2.7.2
 # To retrieve this value, please run the following in your closest shell:
 #
 # $ (cd flutter && git rev-parse HEAD)
-ARG FLUTTER_COMMIT=14f3a36abaace74aeba3e40001ce905336fef415
+ARG FLUTTER_COMMIT=8f7327f83a3e094285163ae402c6f94190fc1674
 
 # We install unzip and remove the apt-index again to keep the
 # docker image diff small.

example/pubspec.yaml

@@ -6,10 +6,10 @@ environment:
   sdk: '>=2.7.0 <3.0.0'
 
 dependencies:
-  codemirror: ^0.5.14
+  codemirror: ^0.5.15
   http: ^0.12.0
 
 dev_dependencies:
-  build_runner: ^1.6.0
-  build_web_compilers: ^2.3.0
-  pedantic: ^1.8.0
+  build_runner: ^1.8.1
+  build_web_compilers: ^2.9.0
+  pedantic: ^1.9.0

flutter

@@ -14,7 +14,7 @@ packages:
       name: _fe_analyzer_shared
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.3"
+    version: "2.1.0"
   analysis_server_lib:
     dependency: "direct main"
     description:
@@ -28,7 +28,7 @@ packages:
       name: analyzer
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.39.4"
+    version: "0.39.6"
   appengine:
     dependency: "direct main"
     description:
@@ -91,7 +91,7 @@ packages:
       name: build_resolvers
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.3.3"
+    version: "1.3.4"
   build_runner:
     dependency: "direct dev"
     description:
@@ -196,7 +196,7 @@ packages:
       name: dart_style
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.3.3"
+    version: "1.3.4"
   dartis:
     dependency: "direct main"
     description:
@@ -329,7 +329,7 @@ packages:
       name: io
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.3.3"
+    version: "0.3.4"
   js:
     dependency: transitive
     description:
@@ -416,13 +416,6 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "1.9.3"
-  package_resolver:
-    dependency: transitive
-    description:
-      name: package_resolver
-      url: "https://pub.dartlang.org"
-    source: hosted
-    version: "1.0.10"
   path:
     dependency: "direct main"
     description: