typo fix in guide

fixes #3308
Remove async from list of Special Attributes so that it is possible to use async=false per issue: #3314
Merge pull request #3316 from wilwade/3315-issue-fix-async

Remove async from list of Special Attributes so that it is possible to u...
Fixed #3283
Fixed #3258
Merge pull request #3319 from nukkumatti/issue-3258

Fixed #3258
Merge pull request #3318 from nukkumatti/issue-3283

Fixed #3283
Better fix for <script async="false"