Improve CI environment

[lambdalisue]

Linux/Mac

• Consider using CircleCI while Travis is way slow
• Run tests with Vim
  • A minimum supported version (8.0.0134)
  • A latest release version (HEAD)
• Run tests with Neovim
  • A minimum supported version (0.1.7)
  • A latest release version (HEAD)

Windows

Not sure the followings are possible while building Vim from source on Windows is painful.

• Run tests with official Vim
  • A minimum supported version or close (8.0.0134)
  • A latest release version or close (HEAD)
• Run tests with Kaoriya Vim
  • A minimum supported version or close (8.0.0134)
  • A latest release version or close (HEAD)
• Run tests with Neovim if possible
  • A minimum supported version (0.1.7)
  • A latest release version (HEAD)

[lambdalisue]

I investigate CircleCI and found that it does not provides Traivs's matrix like feature. So I need to stack on the Travis while the matrix feature is really important for closs-platform test.

[lambdalisue]

25

[lambdalisue]

Closed by #25