fix: handling of one char alias as a camelCase

[coderaiser]

Hi, thank you for a great library :).

I'm using yargs-parser in a lot projects, one of them is redrun (CLI tool to run multiple npm-scripts fast). It has a couple 1 char aliases:

Usage: redrun [...tasks] [options] [-- ...args]
Options:
  -p, --parallel          run scripts in parallel
  -P, --parallel-calm     run scripts in parallel and return zero exit code

After updating to v11.0.0 some of my tests has failed, here is parsing:

const yargsParser = require('yargs-parser');
const result = yargsParser(['-p', 't*'], {
   array: [
     'parallel',
     'parallel-calm'
  ],
  alias: {
    'p': 'parallel',
    'P': 'parallel-calm'
  },
});

console.log(result);

And result:

{ _: [],
  p: [ 't*' ],
  P: [ 't*' ],
  'parallel-calm': [ 't*' ],
  parallelCalm: [ 't*' ],
  parallel: [],
}

the reason was yargs-parser handled p the same as P and parallel-calm, but it is parallel, actually.

The bug is located in condition of extendAliases function:

if (/[A-Z]/.test(x) && configuration['camel-case-expansion']) {
  var c = decamelize(x, '-')
   if (c !== key && flags.aliases[key].indexOf(c) === -1) {
     flags.aliases[key].push(c)
     newAliases[c] = true
   }
}

Which is not makes check of the length of an x, so single char became a camelCase so I added such check.

[bcoe]

@coderaiser thank you for the contribution, sorry for the slow review.