Update minidump-stackwalk to 2021.04.19
Update minidump-stackwalk to 2021.04.19

https://github.com/mozilla-services/minidump-stackwalk/releases/tag/2021.04.19

`18140ad`: Include the list of unloaded modules in the output (#22) (gabrielesvelto)
`dc9ecb5`: Print out subcodes when dealing with __fastfail() exceptions on Windows (gabrielesvelto)
`6d0ace7`: Add the unpacked PGO data to the list of ignored files (gabrielesvelto)
`e91df29`: Make the stackwalker print out the name of NTSTATUS error codes (gabrielesvelto)

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