fix compatibility with commander v7

[gustavkj]

Fixes the code to work with commander v7 (related to #162).

A breaking change is that the command and options have been split up. Example from their changelog:

program
  .command('compress <filename>')
  .option('-t, --trace')
  // Old code before Commander 7
  .action((filename, cmd)) => {
    if (cmd.trace) console.log(`Command name is ${cmd.name()}`);
  });

  // New code
  .action((filename, options, command)) => {
    if (options.trace) console.log(`Command name is ${command.name()}`);
  });

[coveralls]

Pull Request Test Coverage Report for Build 504074647

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

---

Totals
Change from base Build 502871415:	0.0%
Covered Lines:	211
Relevant Lines:	211

---

💛 - Coveralls

[codecov]

Codecov Report

Merging #177 (12b5c9e) into master (fd6803c) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #177   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          216       216           
  Branches        36        36           
=========================================
  Hits           216       216           

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/commands/generate.ts	100.00% <100.00%> (ø)

---

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[gagoar]

we need something that uses the cli so we don't end up here again. much like this so this happens when some API changes. I'm gonna create an issue because is gonna be a bit harder with what we have.