Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/test/utils/introspection/ERC165.test.js

@@ -0,0 +1,11 @@
+const { shouldSupportInterfaces } = require('./SupportsInterface.behavior');
+
+const ERC165 = artifacts.require('$ERC165');
+
+contract('ERC165', function () {
+  beforeEach(async function () {
+    this.mock = await ERC165.new();
+  });
+
+  shouldSupportInterfaces(['ERC165']);
+});