Agniva De Sarker c4b4e1bc38 MM-36271: Bump major version to 6.0 (#17973) ...

https://mattermost.atlassian.net/browse/MM-36271

```release-note
We bump the major version to 6.0
```

2021-07-22 12:21:47 +05:30

..

converters.go

MM-36271: Bump major version to 6.0 (#17973)

2021-07-22 12:21:47 +05:30

main_test.go

MM-36271: Bump major version to 6.0 (#17973)

2021-07-22 12:21:47 +05:30

parsers.go

MM-36271: Bump major version to 6.0 (#17973)

2021-07-22 12:21:47 +05:30

slackimport_test.go

MM-36271: Bump major version to 6.0 (#17973)

2021-07-22 12:21:47 +05:30

slackimport.go

MM-36271: Bump major version to 6.0 (#17973)

2021-07-22 12:21:47 +05:30