Fix extension build warnings

Author: MaximeKjaer

package.json

@@ -55,7 +55,7 @@
         "vscode:publish": "vsce publish --yarn",
         "build": "npm-run-all build:syntax build:extension",
         "build:syntax": "ts-node src/typescript/GenerateTmLanguageFile.ts > ./syntaxes/Scala.tmLanguage.json",
-        "build:extension": "vsce package",
+        "build:extension": "vsce package --yarn",
         "test": "npm-run-all test:*",
         "test:unit": "vscode-tmgrammar-test -s source.scala -g syntaxes/Scala.tmLanguage.json -t 'tests/unit/**/*.test.scala'",
         "test:snap": "vscode-tmgrammar-snap -s source.scala -g syntaxes/Scala.tmLanguage.json -t 'tests/snap/**/*.test.scala'"