Release 15.9.70

• Re-enable eslint-plugin-html (dc0e676)
• Upgrade eslint-plugin-html 5.0.5 -> 6.0.0 (752b326)
• Upgrade gulp-shared-tasks 0.30.7 -> 0.30.8 (acac9da)
• Fix tests with new execa release (8f4f6d1)
• Upgrade execa 1.0.0 -> 2.0.0 (75864c6)
• Upgrade gulp-shared-tasks 0.30.6 -> 0.30.7 (38dbeba)