downgrade to frogeGradle 3.+ from 5.1.+

mixins weren't compiling correctly on the newer version

build.gradle

@@ -1,7 +1,6 @@
 buildscript {
     repositories {
-        maven { url = 'https://files.minecraftforge.net/maven' }
-        jcenter()
+        maven { url = 'https://files.minecraftforge.net' }
         mavenCentral()
         // potential replacement in case of problems:
 		// https://dist.creeper.host/Sponge/maven
@@ -10,7 +9,7 @@ buildscript {
 		maven { url 'https://jitpack.io' }
     }
     dependencies {
-        classpath group: 'net.minecraftforge.gradle', name: 'ForgeGradle', version: '5.1.+', changing: true
+        classpath group: 'net.minecraftforge.gradle', name: 'ForgeGradle', version: '3.+', changing: true
 		classpath group: 'org.spongepowered', name: 'mixingradle', version: '0.7-SNAPSHOT'
     }
 }
@@ -24,7 +23,8 @@ version = 'a1.4.1'
 group = 'com.seibel.lod'
 archivesBaseName = 'lod_1.16.5'
 
-java.toolchain.languageVersion = JavaLanguageVersion.of(8) // Mojang ships Java 8 to end users, so your mod should target Java 8.
+
+sourceCompatibility = targetCompatibility = compileJava.sourceCompatibility = compileJava.targetCompatibility = '1.8' // Need this here so eclipse task generates correctly.
 
 println('Java: ' + System.getProperty('java.version') + ' JVM: ' + System.getProperty('java.vm.version') + '(' + System.getProperty('java.vendor') + ') Arch: ' + System.getProperty('os.arch'))
 minecraft {
@@ -192,7 +192,7 @@ jar {
             "Specification-Title": "LOD",
             "Specification-Version": "1", // We are version 1 of ourselves
             "Implementation-Title": project.name,
-            "Implementation-Version": "{version}",
+            "Implementation-Version": "1",
             "Implementation-Timestamp": new Date().format("yyyy-MM-dd'T'HH:mm:ssZ"),
 			"MixinConfigs": "lod.mixins.json",
         ])
@@ -220,4 +220,4 @@ publishing {
 
 mixin {
     add sourceSets.main, "lod.refmap.json"
-}
+}

gradle/wrapper/gradle-wrapper.properties

@@ -1,5 +1,5 @@
 distributionBase=GRADLE_USER_HOME
 distributionPath=wrapper/dists
-distributionUrl=https\://services.gradle.org/distributions/gradle-7.1.1-bin.zip
 zipStoreBase=GRADLE_USER_HOME
 zipStorePath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-4.10.3-bin.zip