Place tracker/maintenance (#519)

* format place_tracker README

* update sentence in README

* sort Dart members, remove unnecessary type declarations

* Run place_tracker on Android and iOS, update project files

* add link to developer preview caveat

* grammar

* update MAINTENANCE

place_tracker/pubspec.lock

@@ -56,7 +56,7 @@ packages:
       name: crypto
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.1.4"
+    version: "2.1.5"
   cupertino_icons:
     dependency: "direct main"
     description:
@@ -82,7 +82,7 @@ packages:
       name: flutter_plugin_android_lifecycle
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.7"
+    version: "1.0.8"
   flutter_test:
     dependency: "direct dev"
     description: flutter
@@ -94,14 +94,14 @@ packages:
       name: google_maps_flutter
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "0.5.27+1"
+    version: "0.5.30"
   google_maps_flutter_platform_interface:
     dependency: transitive
     description:
       name: google_maps_flutter_platform_interface
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "1.0.1"
+    version: "1.0.4"
   matcher:
     dependency: transitive
     description:
@@ -150,7 +150,7 @@ packages:
       name: provider
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "4.0.5+1"
+    version: "4.3.2"
   sky_engine:
     dependency: transitive
     description: flutter
@@ -218,7 +218,7 @@ packages:
       name: uuid
       url: "https://pub.dartlang.org"
     source: hosted
-    version: "2.0.4"
+    version: "2.2.0"
   vector_math:
     dependency: transitive
     description:
@@ -228,4 +228,4 @@ packages:
     version: "2.0.8"
 sdks:
   dart: ">=2.9.0-14.0.dev <3.0.0"
-  flutter: ">=1.12.13+hotfix.5 <2.0.0"
+  flutter: ">=1.16.3 <2.0.0"