Fix PrettierAsync segmentation fault

[SamHowie]

Summary

This pull request fixes #135 where the command PrettierAsync causes Vim to crash due to segmentation fault.

The following is a summary of the involved fixes:

Transportation fix:

1. Change the jobs in_io back to the default of pipe
2. Read the selected buffer lines and write them to the jobs channel
3. Close the in channel to tell the job we have finished sending

Performance fix:

1. Use a simpler method to delete all lines in the buffer
2. Loop through and append all the lines we want to write to the buffer

Test Plan

Error Reproduction Steps:

1. Copy the crash.js file from @nerfologist reproduction example - https://raw.githubusercontent.com/nerfologist/vim-prettier-async-segv-bug/master/crash.js
2. Open crash.js in vim
3. Execute PrettierAsync
4. Notice the seg fault!

NOTE: If the seg fault doesn't occur, increase the number of lines calling someFunc('something', () => {});. Eventually you will reach your platforms magic buffer size to cause the seg fault.

Test Steps For Fix:

1. Clone pull request commit
2. Copy the crash.js file from @nerfologist reproduction example - https://raw.githubusercontent.com/nerfologist/vim-prettier-async-segv-bug/master/crash.js
3. Open crash.js in vim
4. Execute PrettierAsync
5. Notice there is no seg fault!
6. Make the file much bigger and try again
7. Notice there is still no seg fault!

[SamHowie]

Please note: I have not tested this fix on NeoVim. The only changes that overlap with that code path relate to the performance fixes in s:Apply_Prettier_Format

[mitermayer]

I think this looks good to me feel free to merge this once we test neovim and vim 7.4 sync formatting.

[mitermayer]

I have just tested this out on vim 7.4, vim8 and neovim for regression and most of it worked, the only regression that I noticed is that after your change we seem to get an extra line on the end of the file.

Once that is fixed this should be good to go!

[SamHowie]

I just pushed a fix to remove the extra trailing newline introduced by using the append function.

Looks good on Vim 8. Please confirm Vim 7.4 and NeoVim.

Thanks!

[mitermayer]

Looks good on neovim and vim 7