Increase MSRV to 1.69.0, upgrade nix dev-dependency #84

	on: push

	name: Continuous integration

	jobs:
	ci:
	runs-on: ubuntu-latest
	strategy:
	fail-fast: false
	matrix:
	rust:
	- stable
	- beta
	- nightly
	- 1.69.0 # MSRV

	steps:
	- name: Checkout repo
	uses: actions/checkout@v2

	- name: Setup rust toolchain
	uses: actions-rs/toolchain@v1
	with:
	profile: minimal
	toolchain: ${{ matrix.rust }}
	override: true
	components: rustfmt, clippy

	- name: cargo build
	uses: actions-rs/cargo@v1
	with:
	command: build

	- name: cargo test
	uses: actions-rs/cargo@v1
	with:
	command: test

	- name: cargo fmt
	uses: actions-rs/cargo@v1
	with:
	command: fmt
	args: --all -- --check

	- name: cargo clippy
	uses: actions-rs/cargo@v1
	with:
	command: clippy
	args: -- -D warnings

	semver:
	name: Check semver (must manually inspect)
	runs-on: ubuntu-latest
	steps:
	- uses: actions/checkout@v2

	- name: Check semver (must manually inspect)
	uses: obi1kenobi/cargo-semver-checks-action@v2
	with:
	verbose: true
	continue-on-error: true

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