deps: update libflate requirement from 1.0.0 to 2.1.0 #601

Job	Run time
rustfmt	14s
test (msrv, ubuntu-20.04, 1.77.0)	1m 6s
test (stable, ubuntu-20.04, stable)	1m 18s
test (beta, ubuntu-20.04, beta)	1m 23s
benchmarks	1m 44s
clippy	1m 6s
test (nightly, ubuntu-20.04, nightly)	58s
documentation	1m 13s
test (macos, macos-latest, stable)	1m 8s
test (win-msvc, windows-2019, stable)	3m 4s
Miri	2m 26s
test (win-gnu, windows-2019, stable)	3m 4s
Optional features (approx selected)	33s
Optional features (none selected)	31s
static SuiteSparse (stable, ubuntu-20.04, stable)	37s
static SuiteSparse (macos, macos-latest, stable)	57s
static SuiteSparse (win-msvc, windows-2019, stable)	1m 27s
static SuiteSparse (win-gnu, windows-2019, stable)	1m 25s
	24m 14s

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