Enable and fix lint directives_ordering (#309)

Author: natebosch

analysis_options.yaml

@@ -23,7 +23,7 @@ linter:
   # comment_references
   - control_flow_in_finally
   - curly_braces_in_flow_control_structures
-  # directives_ordering
+  - directives_ordering
   - empty_catches
   - empty_constructor_bodies
   - empty_statements

lib/src/multipart_file.dart

@@ -8,12 +8,11 @@ import 'dart:convert';
 import 'package:http_parser/http_parser.dart';
 
 import 'byte_stream.dart';
-import 'utils.dart';
-
 // ignore: uri_does_not_exist
 import 'multipart_file_stub.dart'
     // ignore: uri_does_not_exist
     if (dart.library.io) 'multipart_file_io.dart';
+import 'utils.dart';
 
 /// A file to be uploaded as part of a [MultipartRequest]. This doesn't need to
 /// correspond to a physical file.

lib/src/streamed_request.dart

@@ -4,8 +4,8 @@
 
 import 'dart:async';
 
-import 'byte_stream.dart';
 import 'base_request.dart';
+import 'byte_stream.dart';
 
 /// An HTTP request where the request body is sent asynchronously after the
 /// connection has been established and the headers have been sent.

lib/src/streamed_response.dart

@@ -4,9 +4,9 @@
 
 import 'dart:async';
 
-import 'byte_stream.dart';
-import 'base_response.dart';
 import 'base_request.dart';
+import 'base_response.dart';
+import 'byte_stream.dart';
 import 'utils.dart';
 
 /// An HTTP response where the response body is received asynchronously after