Drop ghc 8.0.2 support

[rektrex]

Resolves #268

Checklist:

HLint

• I've changed the exposed interface (add new reexports, remove reexports, rename reexported things, etc.).
  • I've updated hlint.dhall accordingly to my changes (add new rules for the new imports, remove old ones, when they are outdated, etc.).
  • I've generated the new .hlint.yaml file (see this instructions).

General

• I've updated the CHANGELOG with the short description of my latest changes.
• All new and existing tests pass.
• I keep the code style used in the files I've changed (see style-guide for more details).
• I've used the stylish-haskell file.
• My change requires the documentation updates.
  • I've updated the documentation accordingly.
• I've added the [ci skip] text to the docs-only related commit's name.

[hint-man]

There is no place for me here... I will choose the truth I like.

[chshersh]

@rektrex It seems that CI for GHC-8.0.2 is failing. Looks like it needs to be removed. Also, not sure, how to verify that there are no remainders in the code without thoroughly looking through the whole codebase 🤔 Unfortunately, diff of what's changed doesn't tell you what else needs to be changed...