Fix .gitignore: stop tracking ignored files

backend/lib/openzeppelin-contracts/contracts/token/ERC777/presets/ERC777PresetFixedSupply.sol

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: MIT
+// OpenZeppelin Contracts v4.4.1 (token/ERC777/presets/ERC777PresetFixedSupply.sol)
+pragma solidity ^0.8.0;
+
+import "../ERC777.sol";
+
+/**
+ * @dev {ERC777} token, including:
+ *
+ *  - Preminted initial supply
+ *  - No access control mechanism (for minting/pausing) and hence no governance
+ *
+ * _Available since v3.4._
+ */
+contract ERC777PresetFixedSupply is ERC777 {
+    /**
+     * @dev Mints `initialSupply` amount of token and transfers them to `owner`.
+     *
+     * See {ERC777-constructor}.
+     */
+    constructor(
+        string memory name,
+        string memory symbol,
+        address[] memory defaultOperators,
+        uint256 initialSupply,
+        address owner
+    ) ERC777(name, symbol, defaultOperators) {
+        _mint(owner, initialSupply, "", "");
+    }
+}