go.mod: bump github.com/mattn/go-isatty from 0.0.19 to 0.0.20 #116

Job	Run time
CI matrix / Assert PR branch is ahead	11s
Makefile / Assert PR branch is ahead	4s
Makefile / Build codebase using Makefile all recipe	0s
Makefile / Lint codebase using Makefile	0s
Makefile / Build codebase using Makefile quick recipe	42s
CI matrix / Build codebase (go-ci-oldstable, false)	36s
CI matrix / Lint codebase (go-ci-oldstable, false)	48s
CI matrix / Build codebase (go-ci-stable, false)	37s
CI matrix / Lint codebase (go-ci-stable, false)	47s
CI matrix / Build codebase (go-ci-unstable, true)	38s
CI matrix / Lint codebase (go-ci-unstable, true)	51s
CI matrix / Run tests (go-ci-oldstable, false)	41s
CI matrix / Run tests (go-ci-stable, false)	47s
CI matrix / Run tests (go-ci-unstable, true)	39s
CI matrix / Optional Linting / Assert PR branch is ahead	4s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-oldstable, true)	50s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-stable, true)	45s
CI matrix / Optional Linting / Lint codebase using optional linters (go-ci-unstable, true)	54s
	9m 54s

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