fix: correct license header references (#882)

See originals:
- https://www.gnu.org/licenses/agpl-3.0.txt
- https://www.gnu.org/licenses/gpl-3.0.txt

desktop/LICENSE

@@ -672,4 +672,3 @@ may consider it more useful to permit linking proprietary applications with
 the library.  If this is what you want to do, use the GNU Lesser General
 Public License instead of this License.  But first, please read
 <https://www.gnu.org/licenses/why-not-lgpl.html>.
-

desktop/build.js

@@ -2,16 +2,16 @@
 // Copyright 2018-present Vikunja and contributors. All rights reserved.
 //
 // This program is free software: you can redistribute it and/or modify
-// it under the terms of the GNU Affero General Public Licensee as published by
+// it under the terms of the GNU Affero General Public License as published by
 // the Free Software Foundation, either version 3 of the License, or
 // (at your option) any later version.
 //
 // This program is distributed in the hope that it will be useful,
 // but WITHOUT ANY WARRANTY; without even the implied warranty of
 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU Affero General Public Licensee for more details.
+// GNU Affero General Public License for more details.
 //
-// You should have received a copy of the GNU Affero General Public Licensee
+// You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
 const fs = require('fs')