Update adblockpluscore to git:56d14b7

Background

For !256 (merged) we need to update adblockpluscore. But this update requires some integration changes for adblockpluscore#278. So let's update to 56d14b7 first.

This bring the following changes (most recent first):

Refs adblockpluscore#278 - Import perf_hooks unconditionally
Fix adblockpluscore#277 - Cleanup synchronizer after each test
Fixed adblockpluscore#278 - Fixed: Importing perf_hooks causes webpack to fail
Noissue - Use relative imports in rsa module
Fixed adblockpluscore#77 - Added new filter option $header
Fixed adblockpluscore#212 - abort-on-iframe-property-read/write snippets
Fixed adblockpluscore#274 - don't use matcher.findKeyword() to map the filter to the keyword
Refs adblockpluscore#239 - Performance benchmark
Fix adblockpluscore#262 - Reduced further the timeout
Fix adblockpluscore#270 - Avoid blocking backup operations on saveToDisk()
Fixed adblockpluscore#266 - Assets and script for resources.json
Fix adblockpluscore#269 - Avoid unnecessary IO.statFile
Fixed adblockpluscore#268 - Bump NodeJS version to Node 12
Fixed adblockpluscore#267 - Provide Synchronizer stop method
Fixed adblockpluscore#259 - Provide a method to bulk-import subscriptions
Fixed adblockpluscore#255 - Update tfjs to 2.7.x
Fixed adblockpluscore#265 - Profile XPath performance
Fixed adblockpluscore#262 - change the onload timeout
Fixed adblockpluscore#263 - Use XPathEvaluator#createExpression
Noissue - Update package-lock.json
Noissue - Bump the semver version of the package
Fixed adblockpluscore#260 - protect used properties in freeze-element
Fixed adblockpluscore#248 - Added Cookies and Notifications recommended subscriptions
Issue adblockpluscore#258 - Added more Norwegian languages for the list subscription
Noissue - freeze-element was in 3.9.5

What to change

Update the submodule
Modify build/tasks/webpack.js to map the perf_hooks module to self