feat (init): Migrating package flutter_sequence_animation to null safetty

.gitignore

@@ -25,7 +25,7 @@
 .dart_tool/
 .flutter-plugins
 .flutter-plugins-dependencies
-.packages
+# .packages
 .pub-cache/
 .pub/
 build/

.packages

+# This file is deprecated. Tools should instead consume 
+# `.dart_tools/package_config.json`.
+# 
+# For more info see: https://dart.dev/go/dot-packages-deprecation
+# 
+# Generated by pub on 2021-06-03 16:00:12.305679.
+async:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/async-2.5.0/lib/
+boolean_selector:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/boolean_selector-2.1.0/lib/
+characters:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/characters-1.1.0/lib/
+charcode:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/charcode-1.2.0/lib/
+clock:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/clock-1.1.0/lib/
+collection:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/collection-1.15.0/lib/
+fake_async:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/fake_async-1.2.0/lib/
+flutter:file:///D:/flutter/2.0.4-stable/packages/flutter/lib/
+flutter_test:file:///D:/flutter/2.0.4-stable/packages/flutter_test/lib/
+matcher:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/matcher-0.12.10/lib/
+meta:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/meta-1.3.0/lib/
+path:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/path-1.8.0/lib/
+sky_engine:file:///D:/flutter/2.0.4-stable/bin/cache/pkg/sky_engine/lib/
+source_span:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/source_span-1.8.0/lib/
+stack_trace:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/stack_trace-1.10.0/lib/
+stream_channel:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/stream_channel-2.1.0/lib/
+string_scanner:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/string_scanner-1.1.0/lib/
+term_glyph:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/term_glyph-1.2.0/lib/
+test_api:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/test_api-0.2.19/lib/
+typed_data:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/typed_data-1.3.0/lib/
+vector_math:file:///D:/flutter/2.0.4-stable/.pub-cache/hosted/pub.dartlang.org/vector_math-2.1.0/lib/
+flutter_sequence_animation_null_safety:lib/