Update SDK constraint to 2.12.0-0 (#38)

Update dependencies and travis config
diff --git a/.travis.yml b/.travis.yml
index b634f67..0ae3250 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,28 +3,10 @@
 dart:
   - dev
 
-jobs:
-  include:
-    - stage: analyze_and_format
-      name: "Analyze"
-      os: linux
-      script: dartanalyzer  --fatal-warnings --fatal-infos .
-    - stage: analyze_and_format
-      name: "Format"
-      os: linux
-      script: dartfmt -n --set-exit-if-changed .
-    - stage: test
-      name: "Vm Tests"
-      os: linux
-      script: pub run --enable-experiment=non-nullable test -p vm
-    - stage: test
-      name: "Web Tests"
-      os: linux
-      script: pub run --enable-experiment=non-nullable test -p chrome
-
-stages:
-  - analyze_and_format
-  - test
+dart_task:
+- dartfmt
+- dartanalyzer: --fatal-warnings --fatal-infos .
+- test: -p vm,chrome
 
 # Only building master means that we don't run two builds for each pull request.
 branches:
diff --git a/pubspec.yaml b/pubspec.yaml
index 03d9ff6..06854b2 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,74 +1,15 @@
 name: convert
 version: 2.2.0-nullsafety-dev
 description: Utilities for converting between data representations.
-homepage: https://github.com/dart-lang/convert
+repository: https://github.com/dart-lang/convert
 
 environment:
-  sdk: '>=2.10.0-2.0.dev <2.11.0'
+  sdk: '>=2.12.0-0 <3.0.0'
 
 dependencies:
-  charcode: ^1.1.0
-  typed_data: ^1.1.0
+  charcode: ^1.2.0-nullsafety.3
+  typed_data: ^1.3.0-nullsafety.5
 
 dev_dependencies:
-  pedantic: ^1.0.0
-  test: ^1.0.0
-
-dependency_overrides:
-  async:
-    git: git://github.com/dart-lang/async.git
-  boolean_selector:
-    git: git://github.com/dart-lang/boolean_selector.git
-  charcode:
-    git: git://github.com/dart-lang/charcode.git
-  collection:
-    git: git://github.com/dart-lang/collection.git
-  js:
-    git:
-      url: git://github.com/dart-lang/sdk.git
-      ref: 2-10-pkgs
-      path: pkg/js
-  matcher:
-    git: git://github.com/dart-lang/matcher.git
-  meta:
-    git:
-      url: git://github.com/dart-lang/sdk.git
-      ref: 2-10-pkgs
-      path: pkg/meta
-  path:
-    git: git://github.com/dart-lang/path.git
-  pedantic:
-    git: git://github.com/dart-lang/pedantic.git
-  pool:
-    git: git://github.com/dart-lang/pool.git
-  source_maps:
-    git: git://github.com/dart-lang/source_maps.git
-  source_map_stack_trace:
-    git: git://github.com/dart-lang/source_map_stack_trace.git
-  source_span:
-    git: git://github.com/dart-lang/source_span.git
-  stack_trace:
-    git: git://github.com/dart-lang/stack_trace.git
-  stream_channel:
-    git: git://github.com/dart-lang/stream_channel.git
-  string_scanner:
-    git: git://github.com/dart-lang/string_scanner.git
-  term_glyph:
-    git: git://github.com/dart-lang/term_glyph.git
-  test_api:
-    git:
-      url: git://github.com/dart-lang/test.git
-      ref: null_safety
-      path: pkgs/test_api
-  test_core:
-    git:
-      url: git://github.com/dart-lang/test.git
-      ref: null_safety
-      path: pkgs/test_core
-  test:
-    git:
-      url: git://github.com/dart-lang/test.git
-      ref: null_safety
-      path: pkgs/test
-  typed_data:
-    git: git://github.com/dart-lang/typed_data.git
+  pedantic: ^1.10.0-nullsafety.3
+  test: ^1.16.0-nullsafety.9