deps: update libflate requirement from 1.0.0 to 2.1.0 #602

Job	Run time
rustfmt	18s
documentation	1m 16s
benchmarks	2m 3s
clippy	59s
Miri	2m 20s
Optional features (approx selected)	34s
Optional features (none selected)	33s
static SuiteSparse (stable, ubuntu-20.04, stable)	35s
static SuiteSparse (macos, macos-latest, stable)	49s
test (msrv, ubuntu-20.04, 1.77.0)	1m 23s
static SuiteSparse (win-msvc, windows-2019, stable)	1m 27s
test (stable, ubuntu-20.04, stable)	1m 3s
test (beta, ubuntu-20.04, beta)	1m 8s
static SuiteSparse (win-gnu, windows-2019, stable)	1m 30s
test (nightly, ubuntu-20.04, nightly)	1m 3s
test (macos, macos-latest, stable)	1m 6s
test (win-msvc, windows-2019, stable)	2m 49s
test (win-gnu, windows-2019, stable)	3m 16s
	24m 12s

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