chromedriver-helper is deprecated

[nard-tech]

chromedriver-helper gem is now deprecated and replaced to titusfortner/webdrivers.

As I reported on #859, I tried to fix broken CI in #858. At the same time I tried to fix this issue (cf. af4d809), but I could not fix entire problems due to other complicated reasons.

cf. https://github.com/ctran/annotate_models/runs/2226549481#step:5:166

Version

• annotate version: 3.1.1
• rails version: 5.2.4.1, 6.0.2.1
• ruby version: 2.4, 2.5, 2.6