Add Rails ~> 6 support

[mzishtiaq]

This PR adds rails ~>6 support.

[mzishtiaq]

Hey @luisalima. 👋 😄

[gr8bit]

@mzishtiaq we should probably all be using this instead of the original outdatedbrowser anyway...
https://github.com/mikemaccana/outdated-browser-rework#readme

[luisalima]

Thanks @mzishtiaq , apologies, my inbox was swamped and I somehow missed this!
@gr8bit thanks for the reference to outdated-browser-rework , didn't know it yet 👍

[gr8bit]

@luisalima Thank you for the merge! Could you publish a new gem as well or should I point my Gemfile to the repo for now?

[mzishtiaq]

@luisalima That's not a problem at all. Thank you!

[mzishtiaq]

@mzishtiaq we should probably all be using this instead of the original outdatedbrowser anyway...
https://github.com/mikemaccana/outdated-browser-rework#readme

You're right! I will see if I can find some time and update this gem so everyone can benefit from it. :)

[luisalima]

@mzishtiaq Just did! Thank you for your help 💙