flutter_svg doesn't compile with Flutter 1.20

[WanjiruCate]

I upgraded to flutter 1.20.0 and my recent projects with flutter_svg don't compile.

Here is the log

`../../../../snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.17.4/lib/src/picture_stream.dart:88:26: Error: Type 'DiagnosticableMixin' not found.
class PictureStream with DiagnosticableMixin {
^^^^^^^^^^^^^^^^^^^
../../../../snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.17.4/lib/src/picture_stream.dart:192:44: Error: Type 'DiagnosticableMixin' not found.
abstract class PictureStreamCompleter with DiagnosticableMixin {
^^^^^^^^^^^^^^^^^^^
../../../../snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.17.4/lib/src/picture_stream.dart:88:7: Error: The type 'DiagnosticableMixin' can't be mixed in.
class PictureStream with DiagnosticableMixin {
^
../../../../snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.17.4/lib/src/picture_stream.dart:192:16: Error: The type 'DiagnosticableMixin' can't be mixed in.
abstract class PictureStreamCompleter with DiagnosticableMixin {
^
../../../../snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.17.4/lib/src/picture_stream.dart:167:11: Error: Superclass has no method named 'debugFillProperties'.
super.debugFillProperties(properties);
^^^^^^^^^^^^^^^^^^^
../../../../snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.17.4/lib/src/picture_stream.dart:171:30: Error: The method 'toStringShort' isn't defined for the class 'PictureStreamCompleter'.

• 'PictureStreamCompleter' is from 'package:flutter_svg/src/picture_stream.dart' ('../../../../snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.17.4/lib/src/picture_stream.dart').
  Try correcting the name to the name of an existing method, or defining a method named 'toStringShort'.
  ifPresent: _completer?.toStringShort(),
  ^^^^^^^^^^^^^
  ../../../../snap/flutter/common/flutter/.pub-cache/hosted/pub.dartlang.org/flutter_svg-0.17.4/lib/src/picture_stream.dart:266:11: Error: Superclass has no method named 'debugFillProperties'.
  super.debugFillProperties(description);
  ^^^^^^^^^^^^^^^^^^^

FAILURE: Build failed with an exception.

• Where:
  Script '/home/wanjiru/snap/flutter/common/flutter/packages/flutter_tools/gradle/flutter.gradle' line: 896

• What went wrong:
  Execution failed for task ':app:compileFlutterBuildDebug'.

Process 'command '/home/wanjiru/snap/flutter/common/flutter/bin/flutter'' finished with non-zero exit value 1

• Try:
  Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

• Get more help at https://help.gradle.org

BUILD FAILED in 33s `

[WanjiruCate]

Flutter pub upgrade did the fix