fix warning from flutter analyze deprecated_member_use

lib/sentry.dart

@@ -197,7 +197,7 @@ class SentryClient {
     List<int> body = utf8.encode(json.encode(data));
     if (compressPayload) {
       headers['Content-Encoding'] = 'gzip';
-      body = GZIP.encode(body);
+      body = gzip.encode(body);
     }
 
     final Response response =

pubspec.yaml

@@ -18,3 +18,5 @@ dev_dependencies:
   test: ">=0.12.0 <2.0.0"
   yaml: ">=2.1.0 <3.0.0"
   mockito: ">=2.0.0 <4.0.0"
+  flutter_test:
+    sdk: flutter

test/sentry_test.dart

@@ -151,12 +151,12 @@ void main() {
 
       Map<String, dynamic> data;
       if (compressPayload) {
-        data = json.decode(utf8.decode(GZIP.decode(body)));
+        data = json.decode(utf8.decode(gzip.decode(body)));
       } else {
         data = json.decode(utf8.decode(body));
       }
       final Map<String, dynamic> stacktrace = data.remove('stacktrace');
-      expect(stacktrace['frames'], const isInstanceOf<List>());
+      expect(stacktrace['frames'], const TypeMatcher<List>());
       expect(stacktrace['frames'], isNotEmpty);
 
       final Map<String, dynamic> topFrame =

test/version_test.dart

@@ -12,7 +12,7 @@ void main() {
   group('sdkVersion', () {
     test('matches that of pubspec.yaml', () {
       final dynamic pubspec =
-          yaml.loadYaml(new File('pubspec.yaml').readAsStringSync());
+          yaml.loadYaml(new File('../pubspec.yaml').readAsStringSync());
       expect(sdkVersion, pubspec['version']);
     });
   });