fix: extendPackage object values should be string

[pksunkara]

Fixes the following issue:

🚀  Invoking generator for vue-cli-plugin-storybook...
 ERROR  TypeError: Cannot read property 'match' of undefined
TypeError: Cannot read property 'match' of undefined
    at resolveDeps (/home/circleci/vue-cli-plugin-storybook/node_modules/@vue/cli/lib/util/mergeDeps.js:14:27)
    at GeneratorAPI.extendPackage (/home/circleci/vue-cli-plugin-storybook/node_modules/@vue/cli/lib/GeneratorAPI.js:195:20)
    at module.exports (/home/circleci/vue-cli-plugin-storybook/tmp/node_modules/vue-cli-plugin-storybook/generator/index.js:9:7)
    at Generator.initPlugins (/home/circleci/vue-cli-plugin-storybook/node_modules/@vue/cli/lib/Generator.js:150:13)
    at Generator.generate (/home/circleci/vue-cli-plugin-storybook/node_modules/@vue/cli/lib/Generator.js:168:16)
    at runGenerator (/home/circleci/vue-cli-plugin-storybook/node_modules/@vue/cli/lib/invoke.js:124:19)
    at process._tickCallback (internal/process/next_tick.js:68:7)

What kind of change does this PR introduce? (check at least one)

• Bugfix
• Feature
• Code style update
• Refactor
• Docs
• Underlying tools
• Other, please describe:

Does this PR introduce a breaking change? (check one)

• Yes
• No

Other information:

[haoqunjiang]

In which case it would be a non-string and why should we accept non-string value?

[pksunkara]

We should kick it up to the package manager. Right now, this is crashing unexpectedly.

[haoqunjiang]

Makes sense. Please add a test here:

vue-cli/packages/@vue/cli/__tests__/Generator.spec.js

Line 259 in 9ec2d34

test('api: warn invalid dep range', async () => {

[pksunkara]

Updated. Before the fix, the test will fail as shown below:

 FAIL  packages/@vue/cli/__tests__/Generator.spec.js
  ● api: warn invalid dep range when non-string

    TypeError: Cannot read property 'match' of null

      13 |     const r2IsString = typeof r2 === 'string'
      14 |     const sourceGeneratorId = sources[name]
    > 15 |     const isValidURI = r2.match(/^(?:file|git|git\+ssh|git\+http|git\+https|git\+file|https?):/) != null
         |                           ^
      16 |     const isValidGitHub = r2IsString && r2.match(/^[^/]+\/[^/]+/) != null
      17 | 
      18 |     // if they are the same, do nothing. Helps when non semver type deps are used

      at mergeDeps (packages/@vue/cli/lib/util/mergeDeps.js:15:27)
      at GeneratorAPI.extendPackage (packages/@vue/cli/lib/GeneratorAPI.js:195:20)
      at apply (packages/@vue/cli/__tests__/Generator.spec.js:288:13)
      at Generator.initPlugins (packages/@vue/cli/lib/Generator.js:150:13)
      at Generator.generate (packages/@vue/cli/lib/Generator.js:168:16)
      at Object.<anonymous> (packages/@vue/cli/__tests__/Generator.spec.js:297:19)

Now, the test will pass.