Update composer/installers from v1 to v2

[adamtomat]

Ticket: #2533

Issue

Bedrock (from Roots) recently upgraded to composer/installers v2 and it makes it very hard to use Timber with Bedrock without also upgrading Timber's dependency.

Solution

Upgrade Timber's "composer/installers" dependency to match Bedrock's (roots/bedrock@43e2a97)

The upstatement/routes package also needs updating before this issue can be resolved.

Impact

Shouldn't have much impact. Anyone who still has a dependency on v1 of composer/installers would be able to use a previously tagged version of Timber if needed.

Considerations

The alternative would be to add support for v1 or v2 like so:
"composer/installers": "~1.0|^2.0"

[coveralls]

Coverage remained the same at 89.774% when pulling 0160425 on adamtomat:2.x-update-composer-installers-dependency into 60d0b31 on timber:2.x.

[gchtr]

Good to go from me. We can merge this in as soon as we fixed the issues with the automated tests.

[jarednova]

Automated tests are now clear — thanks for clearing through that @gchtr.

And thanks as always @adamtomat for this and #2543 to keep us up to date with these Composer dependencies!