Unit test fails on WSL.
```
[Suite] Editor: Send to clipboad
    /home/fox/git/moe/tests/teditor.nim(92, 21): Check failed: exitCode == 0
    exitCode was 1
    /home/fox/git/moe/tests/teditor.nim(94, 43): Check failed: output[0 .. output.high - 1] == $str
    output[0 .. output.high - 1] was xsel: Can't open display: (null)
: Inappropriate ioctl for device
    $str was Clipboard test
  [FAILED] Send string to clipboard 1 (xsel)
    /home/fox/git/moe/tests/teditor.nim(118, 21): Check failed: exitCode == 0
    exitCode was 1
    /home/fox/git/moe/tests/teditor.nim(120, 43): Check failed: output[0 .. output.high - 1] == $str
    output[0 .. output.high - 1] was Error: Can't open display: (null)
    $str was Clipboard test
  [FAILED] Send string to clipboard 1 (xclip)
    /home/fox/git/moe/tests/teditor.nim(144, 21): Check failed: exitCode == 0
    exitCode was 1
    /home/fox/git/moe/tests/teditor.nim(146, 43): Check failed: output[0 .. output.high - 1] == $str
    output[0 .. output.high - 1] was xsel: Can't open display: (null)
: Inappropriate ioctl for device
    $str was `````
  [FAILED] Send string to clipboard 2 (xsel)
    /home/fox/git/moe/tests/teditor.nim(170, 21): Check failed: exitCode == 0
    exitCode was 1
    /home/fox/git/moe/tests/teditor.nim(172, 43): Check failed: output[0 .. output.high - 1] == $str
    output[0 .. output.high - 1] was Error: Can't open display: (null)
    $str was `````
  [FAILED] Send string to clipboard 2 (xclip)
    /home/fox/git/moe/tests/teditor.nim(197, 21): Check failed: exitCode == 0
    exitCode was 1
    /home/fox/git/moe/tests/teditor.nim(199, 43): Check failed: output[0 .. output.high - 1] == $str
    output[0 .. output.high - 1] was xsel: Can't open display: (null)
: Inappropriate ioctl for device
    $str was $Clipboard test
  [FAILED] Send string to clipboard 3 (xsel)
    /home/fox/git/moe/tests/teditor.nim(224, 21): Check failed: exitCode == 0
    exitCode was 1
    /home/fox/git/moe/tests/teditor.nim(226, 43): Check failed: output[0 .. output.high - 1] == $str
    output[0 .. output.high - 1] was Error: Can't open display: (null)
    $str was $Clipboard test
  [FAILED] Send string to clipboard 3 (xclip)
```