Extension causes high cpu load

[pavel-so]

• Issue Type: Performance
• Extension Name: html-css-class-completion
• Extension Version: 1.18.0
• OS Version: Darwin x64 17.7.0
• VSCode version: 1.32.1

⚠️ Make sure to attach this file from your home-directory: /Users/pavshega/Zignd.html-css-class-completion-unresponsive.cpuprofile.txt ⚠️

Find more details here: https://github.com/Microsoft/vscode/wiki/Explain:-extension-causes-high-cpu-load