[BUGFIX] modify VCS repo for t3g/hubspot-forms

Since bitbucket.typo3.com does not exist anymore,
and the package "t3g/hubspot-forms" has been moved
to GitHub, the URL for the VCS section in composer.json
has been adapted.

Process:
- Manually updated the URL (no composer config repositories
  as the current composer.json was modified manually already)
- ran composer update t3g/hubspot-forms

Resolves: 473
4 jobs for feature/473 in 3 minutes and 52 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Test
passed #17902
test:php

00:00:18

passed #17901
test:typoscript

00:00:24

 
  Build
passed #17903
build

00:01:08

 
  Layout
passed #17904
layout

00:02:18