Add vim swap files to .gitignore

[mspang]

Problem

Vim users have a dirty tree while editing files.

Summary of Changes

Add vim swap files to gitignore

[chip-bot]

Size increase report for "Build Examples [nRF]"

File	Section	File	VM

Full report output

Bloat report for job 'Build Examples [nRF]'

Files found only in the baseline:
    bloat_report.txt

Comparing master_binaries/nrf-build/chip-nrf52840-lock-example.out and example_binaries/nrf-build/chip-nrf52840-lock-example.out:

sections,vmsize,filesize

[chip-bot]

Size increase report for "Build Examples [main-build]"

File	Section	File	VM

Full report output

Bloat report for job 'Build Examples [main-build]'

Files found only in the baseline:
    bloat_report.txt

Comparing master_binaries/main-build/chip-standalone-demo.out and example_binaries/main-build/chip-standalone-demo.out:

sections,vmsize,filesize

[chip-bot]

Size increase report for "Build Examples [ESP32]"

File	Section	File	VM
chip-wifi-echo.elf	.flash.text	44	44

Full report output

Bloat report for job 'Build Examples [ESP32]'

Files found only in the baseline:
    bloat_report.txt

Comparing master_binaries/esp32-build/chip-wifi-echo.elf and example_binaries/esp32-build/chip-wifi-echo.elf:

sections,vmsize,filesize
.flash.text,44,44
[Unmapped],0,-4