Freeze the Vue dev dependency to ~2.6

[budnix]

Context

The recently released Vue2 framework with version 2.7 introduced some changes in TypeScript typings that cause errors in our component compiling process. While preparing and testing the fix for the component I've noticed that the change is not backward-compatible, and does not work with Vue <=2.6. The fix needs more time to investigate. That's why this PR proposes a faster fix/workaround. The current version of the component already works in both Vue versions (2.6 and 2.7). To fix the monorepo build workflow I propose to freeze the dev dependencies of the vue and vue-template-compiler packages to ~2.6 (<2.7).

How has this been tested?

I tested the changes locally by executing npm run in vue build command.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Related issue(s):

1. Vue wrapper build script fails with Vue 2.7 #9624

Affected project(s):

• @handsontable/vue

Checklist:

• I have reviewed the guidelines about Contributing to Handsontable and I confirm that my code follows the code style of this project.
• I have signed the Contributor License Agreement

[github-actions]

Launch the local version of documentation by running:

npm run docs:review 33e196c69d3989c787f625b86cd26c0ae055a114