Update 11ty peer dependency

[outsideris]

it is for avoiding upstream dependency conflict.

In mocha, npm install show error with npm@v7 and without package-lock.json.

$ npm install
npm ERR! code ERESOLVE
npm ERR! ERESOLVE unable to resolve dependency tree
npm ERR!
npm ERR! While resolving: mocha@9.0.2
npm ERR! Found: @11ty/eleventy@0.11.1
npm ERR! node_modules/@11ty/eleventy
npm ERR!   dev @11ty/eleventy@"^0.11.0" from the root project
npm ERR!
npm ERR! Could not resolve dependency:
npm ERR! peer @11ty/eleventy@"^0.10.0" from @mocha/docdash@3.0.1
npm ERR! node_modules/@mocha/docdash
npm ERR!   dev @mocha/docdash@"^3.0.1" from the root project
npm ERR!
npm ERR! Fix the upstream dependency conflict, or retry
npm ERR! this command with --force, or --legacy-peer-deps
npm ERR! to accept an incorrect (and potentially broken) dependency resolution.
npm ERR!
npm ERR! See /Users/outsider/.npm/eresolve-report.txt for a full report.

npm ERR! A complete log of this run can be found in:
npm ERR!     /Users/outsider/.npm/_logs/2021-07-26T18_41_03_623Z-debug.log

It's seems npm bug, but I didn't find a root cause. It is related with strict-peer-deps config. Even it's default is false, it works like true.

And there is no problem with npm@v6.

It is not a critical issue, but wh can match peerDependency with mocha.
And we can update 11ty to 0.12.x when we release a new docdash version.