fix: Remove definition of vue-jest as peerDeps

[afontcu]

Partially closes #38

Right now, vue-jest offers two packages to work with Vue 2:

• vue-jest@4, that supports Jest 26.
• @vue/vue2-jest@27, that supports Jest 27.

Since these are different packages, I'm not sure there's a smart way to define the proper peerDep definition (it would be great if it could depend on the installed Jest version).

With npm 7, having the wrong peerDeps means the installation phase will fail.

Thus, I believe not defining any peerDeps is the simplest fix for this problem.

---

Another solution is to mark these packages and optional peerDeps, but I'm not sure this is any better:

"peerDependencies": { 
  "vue-jest": "^4"
},
"peerDependenciesMeta": {
  "vue-jest": {
    "optional": true
  }
}

[afontcu]

(Also – I believe v1-maintain is the right branch to merge commits into because master is aimed to vue 3, right?)

[afontcu]

Thank you @kazupon! And thank you for your hard work