Fix deprecation warning in 1.17/1.18 + update deps

[tmjoen]

Fixed this warning:

==> base62
Compiling 1 file (.ex)
    warning: single-quoted strings represent charlists. Use ~c"" if you indeed want a charlist or use "" instead.
    You may run "mix format --migrate" to fix this warning automatically.
    │
  2 │   use CustomBase, '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'
    │                   ~
    │
    └─ lib/base62.ex:2:19

Also updated test/dev deps to latest version. Bumped required Elixir version to 1.12 (which is still ancient :)) to support newer stream_data dep.

[tmjoen]

We should probably update the Github actions as well since I'd assume this PR will fail on 1.11.x

[mloftis]

Just chiming in a +1 on this.