switch from gitbook to honkit

gitbook is no longer maintained and doesn't work with the latest node/npm

.github/workflows/deploy.yml

@@ -20,15 +20,11 @@ jobs:
         with:
           repository: openfl/AS3ConversionGuide
           path: AS3ConversionGuide
-
-      - name: Install dependencies
-        run: |
-          npm install -g [email protected]
 
       - name: Build
         run: |
-          gitbook build OpenFLDevelopersGuide
-          gitbook build AS3ConversionGuide
+          npx honkit build OpenFLDevelopersGuide
+          npx honkit build AS3ConversionGuide
       
       - name: Prepare deploy
         run: |