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Description
Expected behaviour
highcharts.cachePath or HIGHCHARTS_CACHE_PATH env var should allow an absolute path such as '/tmp/.cache'
Actual behaviour
Previously (v3) if the manifest.json file existed in the 'node_modules/highcharts-export-server/.cache' directory but read-only it would log an error and initPool would continue to start. Now initExport throws an error.
Reproduction steps
Set the 'node_modules/highcharts-export-server/.cache/manifest.json' file as read-only and initExport will throw an error.
Ideally just allow cachePath to specify an absolute path and if the manifest.json file exists (and un-changed) then skip writing new manifest