Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/test/helpers/erc1967.js

@@ -0,0 +1,24 @@
+const ImplementationLabel = 'eip1967.proxy.implementation';
+const AdminLabel = 'eip1967.proxy.admin';
+const BeaconLabel = 'eip1967.proxy.beacon';
+
+function labelToSlot(label) {
+  return '0x' + web3.utils.toBN(web3.utils.keccak256(label)).subn(1).toString(16);
+}
+
+function getSlot(address, slot) {
+  return web3.eth.getStorageAt(
+    web3.utils.isAddress(address) ? address : address.address,
+    web3.utils.isHex(slot) ? slot : labelToSlot(slot),
+  );
+}
+
+module.exports = {
+  ImplementationLabel,
+  AdminLabel,
+  BeaconLabel,
+  ImplementationSlot: labelToSlot(ImplementationLabel),
+  AdminSlot: labelToSlot(AdminLabel),
+  BeaconSlot: labelToSlot(BeaconLabel),
+  getSlot,
+};