Roll flutter_svg (#319)

Roll flutter_svg to a3911bb074c49b821bb9beaa349ee04ac9f4e2f7



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[test-exempt].
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registry/flutter_svg.test

@@ -1,5 +1,5 @@
 [email protected]
 fetch=git clone https://github.com/dnfield/flutter_svg.git tests
-fetch=git -C tests checkout 4c88f8b773f3eaa350876455d134e6cbc183abc4
+fetch=git -C tests checkout a3911bb074c49b821bb9beaa349ee04ac9f4e2f7
 update=packages/flutter_svg
 test.posix=./flutter_test_registry/flutter_test_repo_test.sh