Throw error when --parallel flag is set

[cgewecke]

Initial handling for #98...

(Note: the --parallel flag is not actually supported yet. Pending at hardhat 2359)

[cgewecke]

@fvictorio This is published at an rc tag temporarily (1.0.8-para.0).

yarn add hardhat-gas-reporter@para

(Am going to add a few other things this weekend an publish a patch version sunday or monday.)

[fvictorio]

Hey @cgewecke, thanks for working on this so quickly.

@alcuadrado suggested a better way to approach this: what if, instead of throwing an error, you disable the gas reporter when the --parallel flag is set, and print a warning explaining why? Ideally the warning would be printed at the end, since that's where people will expect to see the coverage.
I think you could do something like this:

subtask(TASK_TEST_RUN_MOCHA_TESTS).setAction(
  async (args: any, hre, runSuper) => {
    if (args.parallel === true) {
      const result = await runSuper()
      // print warning
      return result
    }

[cgewecke]

@fvictorio Oh, yes that is better. Will update.